4616 lines
172 KiB
ReStructuredText
4616 lines
172 KiB
ReStructuredText
.. XXX: reference/datamodel and this have quite a few overlaps!
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.. _bltin-types:
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**************
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Built-in Types
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**************
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The following sections describe the standard types that are built into the
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interpreter.
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.. index:: pair: built-in; types
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The principal built-in types are numerics, sequences, mappings, classes,
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instances and exceptions.
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Some collection classes are mutable. The methods that add, subtract, or
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rearrange their members in place, and don't return a specific item, never return
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the collection instance itself but ``None``.
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Some operations are supported by several object types; in particular,
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practically all objects can be compared, tested for truth value, and converted
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to a string (with the :func:`repr` function or the slightly different
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:func:`str` function). The latter function is implicitly used when an object is
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written by the :func:`print` function.
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.. _truth:
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Truth Value Testing
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===================
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.. index::
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statement: if
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statement: while
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pair: truth; value
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pair: Boolean; operations
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single: false
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Any object can be tested for truth value, for use in an :keyword:`if` or
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:keyword:`while` condition or as operand of the Boolean operations below. The
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following values are considered false:
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.. index:: single: None (Built-in object)
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* ``None``
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.. index:: single: False (Built-in object)
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* ``False``
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* zero of any numeric type, for example, ``0``, ``0.0``, ``0j``.
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* any empty sequence, for example, ``''``, ``()``, ``[]``.
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* any empty mapping, for example, ``{}``.
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* instances of user-defined classes, if the class defines a :meth:`__bool__` or
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:meth:`__len__` method, when that method returns the integer zero or
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:class:`bool` value ``False``. [1]_
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.. index:: single: true
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All other values are considered true --- so objects of many types are always
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true.
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.. index::
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operator: or
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operator: and
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single: False
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single: True
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Operations and built-in functions that have a Boolean result always return ``0``
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or ``False`` for false and ``1`` or ``True`` for true, unless otherwise stated.
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(Important exception: the Boolean operations ``or`` and ``and`` always return
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one of their operands.)
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.. _boolean:
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Boolean Operations --- :keyword:`and`, :keyword:`or`, :keyword:`not`
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====================================================================
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.. index:: pair: Boolean; operations
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These are the Boolean operations, ordered by ascending priority:
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+-------------+---------------------------------+-------+
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| Operation | Result | Notes |
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+=============+=================================+=======+
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| ``x or y`` | if *x* is false, then *y*, else | \(1) |
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| | *x* | |
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+-------------+---------------------------------+-------+
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| ``x and y`` | if *x* is false, then *x*, else | \(2) |
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| | *y* | |
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+-------------+---------------------------------+-------+
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| ``not x`` | if *x* is false, then ``True``, | \(3) |
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| | else ``False`` | |
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+-------------+---------------------------------+-------+
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.. index::
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operator: and
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operator: or
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operator: not
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Notes:
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(1)
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This is a short-circuit operator, so it only evaluates the second
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argument if the first one is :const:`False`.
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(2)
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This is a short-circuit operator, so it only evaluates the second
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argument if the first one is :const:`True`.
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(3)
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``not`` has a lower priority than non-Boolean operators, so ``not a == b`` is
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interpreted as ``not (a == b)``, and ``a == not b`` is a syntax error.
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.. _stdcomparisons:
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Comparisons
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===========
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.. index::
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pair: chaining; comparisons
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pair: operator; comparison
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operator: ==
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operator: <
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operator: <=
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operator: >
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operator: >=
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operator: !=
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operator: is
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operator: is not
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There are eight comparison operations in Python. They all have the same
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priority (which is higher than that of the Boolean operations). Comparisons can
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be chained arbitrarily; for example, ``x < y <= z`` is equivalent to ``x < y and
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y <= z``, except that *y* is evaluated only once (but in both cases *z* is not
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evaluated at all when ``x < y`` is found to be false).
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This table summarizes the comparison operations:
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+------------+-------------------------+
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| Operation | Meaning |
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+============+=========================+
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| ``<`` | strictly less than |
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+------------+-------------------------+
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| ``<=`` | less than or equal |
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+------------+-------------------------+
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| ``>`` | strictly greater than |
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+------------+-------------------------+
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| ``>=`` | greater than or equal |
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+------------+-------------------------+
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| ``==`` | equal |
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+------------+-------------------------+
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| ``!=`` | not equal |
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+------------+-------------------------+
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| ``is`` | object identity |
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+------------+-------------------------+
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| ``is not`` | negated object identity |
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+------------+-------------------------+
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.. index::
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pair: object; numeric
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pair: objects; comparing
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Objects of different types, except different numeric types, never compare equal.
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Furthermore, some types (for example, function objects) support only a degenerate
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notion of comparison where any two objects of that type are unequal. The ``<``,
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``<=``, ``>`` and ``>=`` operators will raise a :exc:`TypeError` exception when
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comparing a complex number with another built-in numeric type, when the objects
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are of different types that cannot be compared, or in other cases where there is
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no defined ordering.
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.. index::
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single: __eq__() (instance method)
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single: __ne__() (instance method)
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single: __lt__() (instance method)
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single: __le__() (instance method)
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single: __gt__() (instance method)
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single: __ge__() (instance method)
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Non-identical instances of a class normally compare as non-equal unless the
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class defines the :meth:`__eq__` method.
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Instances of a class cannot be ordered with respect to other instances of the
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same class, or other types of object, unless the class defines enough of the
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methods :meth:`__lt__`, :meth:`__le__`, :meth:`__gt__`, and :meth:`__ge__` (in
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general, :meth:`__lt__` and :meth:`__eq__` are sufficient, if you want the
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conventional meanings of the comparison operators).
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The behavior of the :keyword:`is` and :keyword:`is not` operators cannot be
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customized; also they can be applied to any two objects and never raise an
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exception.
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.. index::
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operator: in
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operator: not in
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Two more operations with the same syntactic priority, :keyword:`in` and
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:keyword:`not in`, are supported only by sequence types (below).
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.. _typesnumeric:
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Numeric Types --- :class:`int`, :class:`float`, :class:`complex`
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================================================================
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.. index::
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object: numeric
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object: Boolean
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object: integer
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object: floating point
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object: complex number
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pair: C; language
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There are three distinct numeric types: :dfn:`integers`, :dfn:`floating
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point numbers`, and :dfn:`complex numbers`. In addition, Booleans are a
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subtype of integers. Integers have unlimited precision. Floating point
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numbers are usually implemented using :c:type:`double` in C; information
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about the precision and internal representation of floating point
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numbers for the machine on which your program is running is available
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in :data:`sys.float_info`. Complex numbers have a real and imaginary
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part, which are each a floating point number. To extract these parts
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from a complex number *z*, use ``z.real`` and ``z.imag``. (The standard
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library includes additional numeric types, :mod:`fractions` that hold
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rationals, and :mod:`decimal` that hold floating-point numbers with
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user-definable precision.)
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.. index::
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pair: numeric; literals
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pair: integer; literals
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pair: floating point; literals
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pair: complex number; literals
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pair: hexadecimal; literals
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pair: octal; literals
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pair: binary; literals
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Numbers are created by numeric literals or as the result of built-in functions
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and operators. Unadorned integer literals (including hex, octal and binary
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numbers) yield integers. Numeric literals containing a decimal point or an
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exponent sign yield floating point numbers. Appending ``'j'`` or ``'J'`` to a
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numeric literal yields an imaginary number (a complex number with a zero real
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part) which you can add to an integer or float to get a complex number with real
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and imaginary parts.
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.. index::
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single: arithmetic
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builtin: int
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builtin: float
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builtin: complex
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operator: +
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operator: -
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operator: *
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operator: /
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operator: //
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operator: %
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operator: **
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Python fully supports mixed arithmetic: when a binary arithmetic operator has
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operands of different numeric types, the operand with the "narrower" type is
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widened to that of the other, where integer is narrower than floating point,
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which is narrower than complex. Comparisons between numbers of mixed type use
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the same rule. [2]_ The constructors :func:`int`, :func:`float`, and
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:func:`complex` can be used to produce numbers of a specific type.
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All numeric types (except complex) support the following operations, sorted by
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ascending priority (all numeric operations have a higher priority than
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comparison operations):
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+---------------------+---------------------------------+---------+--------------------+
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| Operation | Result | Notes | Full documentation |
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+=====================+=================================+=========+====================+
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| ``x + y`` | sum of *x* and *y* | | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``x - y`` | difference of *x* and *y* | | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``x * y`` | product of *x* and *y* | | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``x / y`` | quotient of *x* and *y* | | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``x // y`` | floored quotient of *x* and | \(1) | |
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| | *y* | | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``x % y`` | remainder of ``x / y`` | \(2) | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``-x`` | *x* negated | | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``+x`` | *x* unchanged | | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``abs(x)`` | absolute value or magnitude of | | :func:`abs` |
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| | *x* | | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``int(x)`` | *x* converted to integer | \(3)\(6)| :func:`int` |
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+---------------------+---------------------------------+---------+--------------------+
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| ``float(x)`` | *x* converted to floating point | \(4)\(6)| :func:`float` |
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+---------------------+---------------------------------+---------+--------------------+
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| ``complex(re, im)`` | a complex number with real part | \(6) | :func:`complex` |
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| | *re*, imaginary part *im*. | | |
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| | *im* defaults to zero. | | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``c.conjugate()`` | conjugate of the complex number | | |
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| | *c* | | |
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+---------------------+---------------------------------+---------+--------------------+
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| ``divmod(x, y)`` | the pair ``(x // y, x % y)`` | \(2) | :func:`divmod` |
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+---------------------+---------------------------------+---------+--------------------+
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| ``pow(x, y)`` | *x* to the power *y* | \(5) | :func:`pow` |
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+---------------------+---------------------------------+---------+--------------------+
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| ``x ** y`` | *x* to the power *y* | \(5) | |
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+---------------------+---------------------------------+---------+--------------------+
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.. index::
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triple: operations on; numeric; types
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single: conjugate() (complex number method)
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Notes:
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(1)
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Also referred to as integer division. The resultant value is a whole
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integer, though the result's type is not necessarily int. The result is
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always rounded towards minus infinity: ``1//2`` is ``0``, ``(-1)//2`` is
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``-1``, ``1//(-2)`` is ``-1``, and ``(-1)//(-2)`` is ``0``.
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(2)
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Not for complex numbers. Instead convert to floats using :func:`abs` if
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appropriate.
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(3)
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.. index::
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module: math
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single: floor() (in module math)
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single: ceil() (in module math)
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single: trunc() (in module math)
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pair: numeric; conversions
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pair: C; language
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Conversion from floating point to integer may round or truncate
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as in C; see functions :func:`math.floor` and :func:`math.ceil` for
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well-defined conversions.
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(4)
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float also accepts the strings "nan" and "inf" with an optional prefix "+"
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or "-" for Not a Number (NaN) and positive or negative infinity.
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(5)
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Python defines ``pow(0, 0)`` and ``0 ** 0`` to be ``1``, as is common for
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programming languages.
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(6)
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The numeric literals accepted include the digits ``0`` to ``9`` or any
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Unicode equivalent (code points with the ``Nd`` property).
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See http://www.unicode.org/Public/8.0.0/ucd/extracted/DerivedNumericType.txt
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for a complete list of code points with the ``Nd`` property.
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All :class:`numbers.Real` types (:class:`int` and :class:`float`) also include
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the following operations:
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+--------------------+------------------------------------+--------+
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| Operation | Result | Notes |
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+====================+====================================+========+
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| ``math.trunc(x)`` | *x* truncated to Integral | |
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+--------------------+------------------------------------+--------+
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| ``round(x[, n])`` | *x* rounded to n digits, | |
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| | rounding half to even. If n is | |
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| | omitted, it defaults to 0. | |
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+--------------------+------------------------------------+--------+
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| ``math.floor(x)`` | the greatest integral float <= *x* | |
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+--------------------+------------------------------------+--------+
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| ``math.ceil(x)`` | the least integral float >= *x* | |
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+--------------------+------------------------------------+--------+
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For additional numeric operations see the :mod:`math` and :mod:`cmath`
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modules.
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.. XXXJH exceptions: overflow (when? what operations?) zerodivision
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.. _bitstring-ops:
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Bitwise Operations on Integer Types
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--------------------------------------
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.. index::
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triple: operations on; integer; types
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pair: bitwise; operations
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pair: shifting; operations
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pair: masking; operations
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operator: ^
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operator: &
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operator: <<
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operator: >>
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Bitwise operations only make sense for integers. Negative numbers are treated
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as their 2's complement value (this assumes a sufficiently large number of bits
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that no overflow occurs during the operation).
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The priorities of the binary bitwise operations are all lower than the numeric
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operations and higher than the comparisons; the unary operation ``~`` has the
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same priority as the other unary numeric operations (``+`` and ``-``).
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This table lists the bitwise operations sorted in ascending priority:
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+------------+--------------------------------+----------+
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| Operation | Result | Notes |
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+============+================================+==========+
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| ``x | y`` | bitwise :dfn:`or` of *x* and | |
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| | *y* | |
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+------------+--------------------------------+----------+
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| ``x ^ y`` | bitwise :dfn:`exclusive or` of | |
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| | *x* and *y* | |
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+------------+--------------------------------+----------+
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| ``x & y`` | bitwise :dfn:`and` of *x* and | |
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| | *y* | |
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+------------+--------------------------------+----------+
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| ``x << n`` | *x* shifted left by *n* bits | (1)(2) |
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+------------+--------------------------------+----------+
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| ``x >> n`` | *x* shifted right by *n* bits | (1)(3) |
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+------------+--------------------------------+----------+
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| ``~x`` | the bits of *x* inverted | |
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+------------+--------------------------------+----------+
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Notes:
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(1)
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Negative shift counts are illegal and cause a :exc:`ValueError` to be raised.
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(2)
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A left shift by *n* bits is equivalent to multiplication by ``pow(2, n)``
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without overflow check.
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(3)
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A right shift by *n* bits is equivalent to division by ``pow(2, n)`` without
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overflow check.
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Additional Methods on Integer Types
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-----------------------------------
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The int type implements the :class:`numbers.Integral` :term:`abstract base
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class`. In addition, it provides a few more methods:
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.. method:: int.bit_length()
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Return the number of bits necessary to represent an integer in binary,
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excluding the sign and leading zeros::
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>>> n = -37
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>>> bin(n)
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'-0b100101'
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>>> n.bit_length()
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6
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More precisely, if ``x`` is nonzero, then ``x.bit_length()`` is the
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unique positive integer ``k`` such that ``2**(k-1) <= abs(x) < 2**k``.
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Equivalently, when ``abs(x)`` is small enough to have a correctly
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rounded logarithm, then ``k = 1 + int(log(abs(x), 2))``.
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If ``x`` is zero, then ``x.bit_length()`` returns ``0``.
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Equivalent to::
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def bit_length(self):
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s = bin(self) # binary representation: bin(-37) --> '-0b100101'
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s = s.lstrip('-0b') # remove leading zeros and minus sign
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return len(s) # len('100101') --> 6
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.. versionadded:: 3.1
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.. method:: int.to_bytes(length, byteorder, \*, signed=False)
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Return an array of bytes representing an integer.
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>>> (1024).to_bytes(2, byteorder='big')
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b'\x04\x00'
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>>> (1024).to_bytes(10, byteorder='big')
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b'\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00'
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>>> (-1024).to_bytes(10, byteorder='big', signed=True)
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b'\xff\xff\xff\xff\xff\xff\xff\xff\xfc\x00'
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>>> x = 1000
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>>> x.to_bytes((x.bit_length() // 8) + 1, byteorder='little')
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b'\xe8\x03'
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The integer is represented using *length* bytes. An :exc:`OverflowError`
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is raised if the integer is not representable with the given number of
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bytes.
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The *byteorder* argument determines the byte order used to represent the
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integer. If *byteorder* is ``"big"``, the most significant byte is at the
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beginning of the byte array. If *byteorder* is ``"little"``, the most
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significant byte is at the end of the byte array. To request the native
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byte order of the host system, use :data:`sys.byteorder` as the byte order
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value.
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The *signed* argument determines whether two's complement is used to
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represent the integer. If *signed* is ``False`` and a negative integer is
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given, an :exc:`OverflowError` is raised. The default value for *signed*
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is ``False``.
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.. versionadded:: 3.2
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.. classmethod:: int.from_bytes(bytes, byteorder, \*, signed=False)
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Return the integer represented by the given array of bytes.
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>>> int.from_bytes(b'\x00\x10', byteorder='big')
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|
16
|
|
>>> int.from_bytes(b'\x00\x10', byteorder='little')
|
|
4096
|
|
>>> int.from_bytes(b'\xfc\x00', byteorder='big', signed=True)
|
|
-1024
|
|
>>> int.from_bytes(b'\xfc\x00', byteorder='big', signed=False)
|
|
64512
|
|
>>> int.from_bytes([255, 0, 0], byteorder='big')
|
|
16711680
|
|
|
|
The argument *bytes* must either be a :term:`bytes-like object` or an
|
|
iterable producing bytes.
|
|
|
|
The *byteorder* argument determines the byte order used to represent the
|
|
integer. If *byteorder* is ``"big"``, the most significant byte is at the
|
|
beginning of the byte array. If *byteorder* is ``"little"``, the most
|
|
significant byte is at the end of the byte array. To request the native
|
|
byte order of the host system, use :data:`sys.byteorder` as the byte order
|
|
value.
|
|
|
|
The *signed* argument indicates whether two's complement is used to
|
|
represent the integer.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
Additional Methods on Float
|
|
---------------------------
|
|
|
|
The float type implements the :class:`numbers.Real` :term:`abstract base
|
|
class`. float also has the following additional methods.
|
|
|
|
.. method:: float.as_integer_ratio()
|
|
|
|
Return a pair of integers whose ratio is exactly equal to the
|
|
original float and with a positive denominator. Raises
|
|
:exc:`OverflowError` on infinities and a :exc:`ValueError` on
|
|
NaNs.
|
|
|
|
.. method:: float.is_integer()
|
|
|
|
Return ``True`` if the float instance is finite with integral
|
|
value, and ``False`` otherwise::
|
|
|
|
>>> (-2.0).is_integer()
|
|
True
|
|
>>> (3.2).is_integer()
|
|
False
|
|
|
|
Two methods support conversion to
|
|
and from hexadecimal strings. Since Python's floats are stored
|
|
internally as binary numbers, converting a float to or from a
|
|
*decimal* string usually involves a small rounding error. In
|
|
contrast, hexadecimal strings allow exact representation and
|
|
specification of floating-point numbers. This can be useful when
|
|
debugging, and in numerical work.
|
|
|
|
|
|
.. method:: float.hex()
|
|
|
|
Return a representation of a floating-point number as a hexadecimal
|
|
string. For finite floating-point numbers, this representation
|
|
will always include a leading ``0x`` and a trailing ``p`` and
|
|
exponent.
|
|
|
|
|
|
.. classmethod:: float.fromhex(s)
|
|
|
|
Class method to return the float represented by a hexadecimal
|
|
string *s*. The string *s* may have leading and trailing
|
|
whitespace.
|
|
|
|
|
|
Note that :meth:`float.hex` is an instance method, while
|
|
:meth:`float.fromhex` is a class method.
|
|
|
|
A hexadecimal string takes the form::
|
|
|
|
[sign] ['0x'] integer ['.' fraction] ['p' exponent]
|
|
|
|
where the optional ``sign`` may by either ``+`` or ``-``, ``integer``
|
|
and ``fraction`` are strings of hexadecimal digits, and ``exponent``
|
|
is a decimal integer with an optional leading sign. Case is not
|
|
significant, and there must be at least one hexadecimal digit in
|
|
either the integer or the fraction. This syntax is similar to the
|
|
syntax specified in section 6.4.4.2 of the C99 standard, and also to
|
|
the syntax used in Java 1.5 onwards. In particular, the output of
|
|
:meth:`float.hex` is usable as a hexadecimal floating-point literal in
|
|
C or Java code, and hexadecimal strings produced by C's ``%a`` format
|
|
character or Java's ``Double.toHexString`` are accepted by
|
|
:meth:`float.fromhex`.
|
|
|
|
|
|
Note that the exponent is written in decimal rather than hexadecimal,
|
|
and that it gives the power of 2 by which to multiply the coefficient.
|
|
For example, the hexadecimal string ``0x3.a7p10`` represents the
|
|
floating-point number ``(3 + 10./16 + 7./16**2) * 2.0**10``, or
|
|
``3740.0``::
|
|
|
|
>>> float.fromhex('0x3.a7p10')
|
|
3740.0
|
|
|
|
|
|
Applying the reverse conversion to ``3740.0`` gives a different
|
|
hexadecimal string representing the same number::
|
|
|
|
>>> float.hex(3740.0)
|
|
'0x1.d380000000000p+11'
|
|
|
|
|
|
.. _numeric-hash:
|
|
|
|
Hashing of numeric types
|
|
------------------------
|
|
|
|
For numbers ``x`` and ``y``, possibly of different types, it's a requirement
|
|
that ``hash(x) == hash(y)`` whenever ``x == y`` (see the :meth:`__hash__`
|
|
method documentation for more details). For ease of implementation and
|
|
efficiency across a variety of numeric types (including :class:`int`,
|
|
:class:`float`, :class:`decimal.Decimal` and :class:`fractions.Fraction`)
|
|
Python's hash for numeric types is based on a single mathematical function
|
|
that's defined for any rational number, and hence applies to all instances of
|
|
:class:`int` and :class:`fractions.Fraction`, and all finite instances of
|
|
:class:`float` and :class:`decimal.Decimal`. Essentially, this function is
|
|
given by reduction modulo ``P`` for a fixed prime ``P``. The value of ``P`` is
|
|
made available to Python as the :attr:`modulus` attribute of
|
|
:data:`sys.hash_info`.
|
|
|
|
.. impl-detail::
|
|
|
|
Currently, the prime used is ``P = 2**31 - 1`` on machines with 32-bit C
|
|
longs and ``P = 2**61 - 1`` on machines with 64-bit C longs.
|
|
|
|
Here are the rules in detail:
|
|
|
|
- If ``x = m / n`` is a nonnegative rational number and ``n`` is not divisible
|
|
by ``P``, define ``hash(x)`` as ``m * invmod(n, P) % P``, where ``invmod(n,
|
|
P)`` gives the inverse of ``n`` modulo ``P``.
|
|
|
|
- If ``x = m / n`` is a nonnegative rational number and ``n`` is
|
|
divisible by ``P`` (but ``m`` is not) then ``n`` has no inverse
|
|
modulo ``P`` and the rule above doesn't apply; in this case define
|
|
``hash(x)`` to be the constant value ``sys.hash_info.inf``.
|
|
|
|
- If ``x = m / n`` is a negative rational number define ``hash(x)``
|
|
as ``-hash(-x)``. If the resulting hash is ``-1``, replace it with
|
|
``-2``.
|
|
|
|
- The particular values ``sys.hash_info.inf``, ``-sys.hash_info.inf``
|
|
and ``sys.hash_info.nan`` are used as hash values for positive
|
|
infinity, negative infinity, or nans (respectively). (All hashable
|
|
nans have the same hash value.)
|
|
|
|
- For a :class:`complex` number ``z``, the hash values of the real
|
|
and imaginary parts are combined by computing ``hash(z.real) +
|
|
sys.hash_info.imag * hash(z.imag)``, reduced modulo
|
|
``2**sys.hash_info.width`` so that it lies in
|
|
``range(-2**(sys.hash_info.width - 1), 2**(sys.hash_info.width -
|
|
1))``. Again, if the result is ``-1``, it's replaced with ``-2``.
|
|
|
|
|
|
To clarify the above rules, here's some example Python code,
|
|
equivalent to the built-in hash, for computing the hash of a rational
|
|
number, :class:`float`, or :class:`complex`::
|
|
|
|
|
|
import sys, math
|
|
|
|
def hash_fraction(m, n):
|
|
"""Compute the hash of a rational number m / n.
|
|
|
|
Assumes m and n are integers, with n positive.
|
|
Equivalent to hash(fractions.Fraction(m, n)).
|
|
|
|
"""
|
|
P = sys.hash_info.modulus
|
|
# Remove common factors of P. (Unnecessary if m and n already coprime.)
|
|
while m % P == n % P == 0:
|
|
m, n = m // P, n // P
|
|
|
|
if n % P == 0:
|
|
hash_ = sys.hash_info.inf
|
|
else:
|
|
# Fermat's Little Theorem: pow(n, P-1, P) is 1, so
|
|
# pow(n, P-2, P) gives the inverse of n modulo P.
|
|
hash_ = (abs(m) % P) * pow(n, P - 2, P) % P
|
|
if m < 0:
|
|
hash_ = -hash_
|
|
if hash_ == -1:
|
|
hash_ = -2
|
|
return hash_
|
|
|
|
def hash_float(x):
|
|
"""Compute the hash of a float x."""
|
|
|
|
if math.isnan(x):
|
|
return sys.hash_info.nan
|
|
elif math.isinf(x):
|
|
return sys.hash_info.inf if x > 0 else -sys.hash_info.inf
|
|
else:
|
|
return hash_fraction(*x.as_integer_ratio())
|
|
|
|
def hash_complex(z):
|
|
"""Compute the hash of a complex number z."""
|
|
|
|
hash_ = hash_float(z.real) + sys.hash_info.imag * hash_float(z.imag)
|
|
# do a signed reduction modulo 2**sys.hash_info.width
|
|
M = 2**(sys.hash_info.width - 1)
|
|
hash_ = (hash_ & (M - 1)) - (hash & M)
|
|
if hash_ == -1:
|
|
hash_ == -2
|
|
return hash_
|
|
|
|
.. _typeiter:
|
|
|
|
Iterator Types
|
|
==============
|
|
|
|
.. index::
|
|
single: iterator protocol
|
|
single: protocol; iterator
|
|
single: sequence; iteration
|
|
single: container; iteration over
|
|
|
|
Python supports a concept of iteration over containers. This is implemented
|
|
using two distinct methods; these are used to allow user-defined classes to
|
|
support iteration. Sequences, described below in more detail, always support
|
|
the iteration methods.
|
|
|
|
One method needs to be defined for container objects to provide iteration
|
|
support:
|
|
|
|
.. XXX duplicated in reference/datamodel!
|
|
|
|
.. method:: container.__iter__()
|
|
|
|
Return an iterator object. The object is required to support the iterator
|
|
protocol described below. If a container supports different types of
|
|
iteration, additional methods can be provided to specifically request
|
|
iterators for those iteration types. (An example of an object supporting
|
|
multiple forms of iteration would be a tree structure which supports both
|
|
breadth-first and depth-first traversal.) This method corresponds to the
|
|
:c:member:`~PyTypeObject.tp_iter` slot of the type structure for Python objects in the Python/C
|
|
API.
|
|
|
|
The iterator objects themselves are required to support the following two
|
|
methods, which together form the :dfn:`iterator protocol`:
|
|
|
|
|
|
.. method:: iterator.__iter__()
|
|
|
|
Return the iterator object itself. This is required to allow both containers
|
|
and iterators to be used with the :keyword:`for` and :keyword:`in` statements.
|
|
This method corresponds to the :c:member:`~PyTypeObject.tp_iter` slot of the type structure for
|
|
Python objects in the Python/C API.
|
|
|
|
|
|
.. method:: iterator.__next__()
|
|
|
|
Return the next item from the container. If there are no further items, raise
|
|
the :exc:`StopIteration` exception. This method corresponds to the
|
|
:c:member:`~PyTypeObject.tp_iternext` slot of the type structure for Python objects in the
|
|
Python/C API.
|
|
|
|
Python defines several iterator objects to support iteration over general and
|
|
specific sequence types, dictionaries, and other more specialized forms. The
|
|
specific types are not important beyond their implementation of the iterator
|
|
protocol.
|
|
|
|
Once an iterator's :meth:`~iterator.__next__` method raises
|
|
:exc:`StopIteration`, it must continue to do so on subsequent calls.
|
|
Implementations that do not obey this property are deemed broken.
|
|
|
|
|
|
.. _generator-types:
|
|
|
|
Generator Types
|
|
---------------
|
|
|
|
Python's :term:`generator`\s provide a convenient way to implement the iterator
|
|
protocol. If a container object's :meth:`__iter__` method is implemented as a
|
|
generator, it will automatically return an iterator object (technically, a
|
|
generator object) supplying the :meth:`__iter__` and :meth:`~generator.__next__`
|
|
methods.
|
|
More information about generators can be found in :ref:`the documentation for
|
|
the yield expression <yieldexpr>`.
|
|
|
|
|
|
.. _typesseq:
|
|
|
|
Sequence Types --- :class:`list`, :class:`tuple`, :class:`range`
|
|
================================================================
|
|
|
|
There are three basic sequence types: lists, tuples, and range objects.
|
|
Additional sequence types tailored for processing of
|
|
:ref:`binary data <binaryseq>` and :ref:`text strings <textseq>` are
|
|
described in dedicated sections.
|
|
|
|
|
|
.. _typesseq-common:
|
|
|
|
Common Sequence Operations
|
|
--------------------------
|
|
|
|
.. index:: object: sequence
|
|
|
|
The operations in the following table are supported by most sequence types,
|
|
both mutable and immutable. The :class:`collections.abc.Sequence` ABC is
|
|
provided to make it easier to correctly implement these operations on
|
|
custom sequence types.
|
|
|
|
This table lists the sequence operations sorted in ascending priority. In the
|
|
table, *s* and *t* are sequences of the same type, *n*, *i*, *j* and *k* are
|
|
integers and *x* is an arbitrary object that meets any type and value
|
|
restrictions imposed by *s*.
|
|
|
|
The ``in`` and ``not in`` operations have the same priorities as the
|
|
comparison operations. The ``+`` (concatenation) and ``*`` (repetition)
|
|
operations have the same priority as the corresponding numeric operations.
|
|
|
|
.. index::
|
|
triple: operations on; sequence; types
|
|
builtin: len
|
|
builtin: min
|
|
builtin: max
|
|
pair: concatenation; operation
|
|
pair: repetition; operation
|
|
pair: subscript; operation
|
|
pair: slice; operation
|
|
operator: in
|
|
operator: not in
|
|
single: count() (sequence method)
|
|
single: index() (sequence method)
|
|
|
|
+--------------------------+--------------------------------+----------+
|
|
| Operation | Result | Notes |
|
|
+==========================+================================+==========+
|
|
| ``x in s`` | ``True`` if an item of *s* is | \(1) |
|
|
| | equal to *x*, else ``False`` | |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``x not in s`` | ``False`` if an item of *s* is | \(1) |
|
|
| | equal to *x*, else ``True`` | |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``s + t`` | the concatenation of *s* and | (6)(7) |
|
|
| | *t* | |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``s * n`` or | equivalent to adding *s* to | (2)(7) |
|
|
| ``n * s`` | itself *n* times | |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``s[i]`` | *i*\ th item of *s*, origin 0 | \(3) |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``s[i:j]`` | slice of *s* from *i* to *j* | (3)(4) |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``s[i:j:k]`` | slice of *s* from *i* to *j* | (3)(5) |
|
|
| | with step *k* | |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``len(s)`` | length of *s* | |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``min(s)`` | smallest item of *s* | |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``max(s)`` | largest item of *s* | |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``s.index(x[, i[, j]])`` | index of the first occurrence | \(8) |
|
|
| | of *x* in *s* (at or after | |
|
|
| | index *i* and before index *j*)| |
|
|
+--------------------------+--------------------------------+----------+
|
|
| ``s.count(x)`` | total number of occurrences of | |
|
|
| | *x* in *s* | |
|
|
+--------------------------+--------------------------------+----------+
|
|
|
|
Sequences of the same type also support comparisons. In particular, tuples
|
|
and lists are compared lexicographically by comparing corresponding elements.
|
|
This means that to compare equal, every element must compare equal and the
|
|
two sequences must be of the same type and have the same length. (For full
|
|
details see :ref:`comparisons` in the language reference.)
|
|
|
|
Notes:
|
|
|
|
(1)
|
|
While the ``in`` and ``not in`` operations are used only for simple
|
|
containment testing in the general case, some specialised sequences
|
|
(such as :class:`str`, :class:`bytes` and :class:`bytearray`) also use
|
|
them for subsequence testing::
|
|
|
|
>>> "gg" in "eggs"
|
|
True
|
|
|
|
(2)
|
|
Values of *n* less than ``0`` are treated as ``0`` (which yields an empty
|
|
sequence of the same type as *s*). Note that items in the sequence *s*
|
|
are not copied; they are referenced multiple times. This often haunts
|
|
new Python programmers; consider::
|
|
|
|
>>> lists = [[]] * 3
|
|
>>> lists
|
|
[[], [], []]
|
|
>>> lists[0].append(3)
|
|
>>> lists
|
|
[[3], [3], [3]]
|
|
|
|
What has happened is that ``[[]]`` is a one-element list containing an empty
|
|
list, so all three elements of ``[[]] * 3`` are references to this single empty
|
|
list. Modifying any of the elements of ``lists`` modifies this single list.
|
|
You can create a list of different lists this way::
|
|
|
|
>>> lists = [[] for i in range(3)]
|
|
>>> lists[0].append(3)
|
|
>>> lists[1].append(5)
|
|
>>> lists[2].append(7)
|
|
>>> lists
|
|
[[3], [5], [7]]
|
|
|
|
Further explanation is available in the FAQ entry
|
|
:ref:`faq-multidimensional-list`.
|
|
|
|
(3)
|
|
If *i* or *j* is negative, the index is relative to the end of the string:
|
|
``len(s) + i`` or ``len(s) + j`` is substituted. But note that ``-0`` is
|
|
still ``0``.
|
|
|
|
(4)
|
|
The slice of *s* from *i* to *j* is defined as the sequence of items with index
|
|
*k* such that ``i <= k < j``. If *i* or *j* is greater than ``len(s)``, use
|
|
``len(s)``. If *i* is omitted or ``None``, use ``0``. If *j* is omitted or
|
|
``None``, use ``len(s)``. If *i* is greater than or equal to *j*, the slice is
|
|
empty.
|
|
|
|
(5)
|
|
The slice of *s* from *i* to *j* with step *k* is defined as the sequence of
|
|
items with index ``x = i + n*k`` such that ``0 <= n < (j-i)/k``. In other words,
|
|
the indices are ``i``, ``i+k``, ``i+2*k``, ``i+3*k`` and so on, stopping when
|
|
*j* is reached (but never including *j*). If *i* or *j* is greater than
|
|
``len(s)``, use ``len(s)``. If *i* or *j* are omitted or ``None``, they become
|
|
"end" values (which end depends on the sign of *k*). Note, *k* cannot be zero.
|
|
If *k* is ``None``, it is treated like ``1``.
|
|
|
|
(6)
|
|
Concatenating immutable sequences always results in a new object. This
|
|
means that building up a sequence by repeated concatenation will have a
|
|
quadratic runtime cost in the total sequence length. To get a linear
|
|
runtime cost, you must switch to one of the alternatives below:
|
|
|
|
* if concatenating :class:`str` objects, you can build a list and use
|
|
:meth:`str.join` at the end or else write to a :class:`io.StringIO`
|
|
instance and retrieve its value when complete
|
|
|
|
* if concatenating :class:`bytes` objects, you can similarly use
|
|
:meth:`bytes.join` or :class:`io.BytesIO`, or you can do in-place
|
|
concatenation with a :class:`bytearray` object. :class:`bytearray`
|
|
objects are mutable and have an efficient overallocation mechanism
|
|
|
|
* if concatenating :class:`tuple` objects, extend a :class:`list` instead
|
|
|
|
* for other types, investigate the relevant class documentation
|
|
|
|
|
|
(7)
|
|
Some sequence types (such as :class:`range`) only support item sequences
|
|
that follow specific patterns, and hence don't support sequence
|
|
concatenation or repetition.
|
|
|
|
(8)
|
|
``index`` raises :exc:`ValueError` when *x* is not found in *s*.
|
|
When supported, the additional arguments to the index method allow
|
|
efficient searching of subsections of the sequence. Passing the extra
|
|
arguments is roughly equivalent to using ``s[i:j].index(x)``, only
|
|
without copying any data and with the returned index being relative to
|
|
the start of the sequence rather than the start of the slice.
|
|
|
|
|
|
.. _typesseq-immutable:
|
|
|
|
Immutable Sequence Types
|
|
------------------------
|
|
|
|
.. index::
|
|
triple: immutable; sequence; types
|
|
object: tuple
|
|
builtin: hash
|
|
|
|
The only operation that immutable sequence types generally implement that is
|
|
not also implemented by mutable sequence types is support for the :func:`hash`
|
|
built-in.
|
|
|
|
This support allows immutable sequences, such as :class:`tuple` instances, to
|
|
be used as :class:`dict` keys and stored in :class:`set` and :class:`frozenset`
|
|
instances.
|
|
|
|
Attempting to hash an immutable sequence that contains unhashable values will
|
|
result in :exc:`TypeError`.
|
|
|
|
|
|
.. _typesseq-mutable:
|
|
|
|
Mutable Sequence Types
|
|
----------------------
|
|
|
|
.. index::
|
|
triple: mutable; sequence; types
|
|
object: list
|
|
object: bytearray
|
|
|
|
The operations in the following table are defined on mutable sequence types.
|
|
The :class:`collections.abc.MutableSequence` ABC is provided to make it
|
|
easier to correctly implement these operations on custom sequence types.
|
|
|
|
In the table *s* is an instance of a mutable sequence type, *t* is any
|
|
iterable object and *x* is an arbitrary object that meets any type
|
|
and value restrictions imposed by *s* (for example, :class:`bytearray` only
|
|
accepts integers that meet the value restriction ``0 <= x <= 255``).
|
|
|
|
|
|
.. index::
|
|
triple: operations on; sequence; types
|
|
triple: operations on; list; type
|
|
pair: subscript; assignment
|
|
pair: slice; assignment
|
|
statement: del
|
|
single: append() (sequence method)
|
|
single: clear() (sequence method)
|
|
single: copy() (sequence method)
|
|
single: extend() (sequence method)
|
|
single: insert() (sequence method)
|
|
single: pop() (sequence method)
|
|
single: remove() (sequence method)
|
|
single: reverse() (sequence method)
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| Operation | Result | Notes |
|
|
+==============================+================================+=====================+
|
|
| ``s[i] = x`` | item *i* of *s* is replaced by | |
|
|
| | *x* | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``s[i:j] = t`` | slice of *s* from *i* to *j* | |
|
|
| | is replaced by the contents of | |
|
|
| | the iterable *t* | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``del s[i:j]`` | same as ``s[i:j] = []`` | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``s[i:j:k] = t`` | the elements of ``s[i:j:k]`` | \(1) |
|
|
| | are replaced by those of *t* | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``del s[i:j:k]`` | removes the elements of | |
|
|
| | ``s[i:j:k]`` from the list | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``s.append(x)`` | appends *x* to the end of the | |
|
|
| | sequence (same as | |
|
|
| | ``s[len(s):len(s)] = [x]``) | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``s.clear()`` | removes all items from ``s`` | \(5) |
|
|
| | (same as ``del s[:]``) | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``s.copy()`` | creates a shallow copy of ``s``| \(5) |
|
|
| | (same as ``s[:]``) | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``s.extend(t)`` | extends *s* with the | |
|
|
| | contents of *t* (same as | |
|
|
| | ``s[len(s):len(s)] = t``) | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``s.insert(i, x)`` | inserts *x* into *s* at the | |
|
|
| | index given by *i* | |
|
|
| | (same as ``s[i:i] = [x]``) | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``s.pop([i])`` | retrieves the item at *i* and | \(2) |
|
|
| | also removes it from *s* | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``s.remove(x)`` | remove the first item from *s* | \(3) |
|
|
| | where ``s[i] == x`` | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
| ``s.reverse()`` | reverses the items of *s* in | \(4) |
|
|
| | place | |
|
|
+------------------------------+--------------------------------+---------------------+
|
|
|
|
|
|
Notes:
|
|
|
|
(1)
|
|
*t* must have the same length as the slice it is replacing.
|
|
|
|
(2)
|
|
The optional argument *i* defaults to ``-1``, so that by default the last
|
|
item is removed and returned.
|
|
|
|
(3)
|
|
``remove`` raises :exc:`ValueError` when *x* is not found in *s*.
|
|
|
|
(4)
|
|
The :meth:`reverse` method modifies the sequence in place for economy of
|
|
space when reversing a large sequence. To remind users that it operates by
|
|
side effect, it does not return the reversed sequence.
|
|
|
|
(5)
|
|
:meth:`clear` and :meth:`!copy` are included for consistency with the
|
|
interfaces of mutable containers that don't support slicing operations
|
|
(such as :class:`dict` and :class:`set`)
|
|
|
|
.. versionadded:: 3.3
|
|
:meth:`clear` and :meth:`!copy` methods.
|
|
|
|
|
|
.. _typesseq-list:
|
|
|
|
Lists
|
|
-----
|
|
|
|
.. index:: object: list
|
|
|
|
Lists are mutable sequences, typically used to store collections of
|
|
homogeneous items (where the precise degree of similarity will vary by
|
|
application).
|
|
|
|
.. class:: list([iterable])
|
|
|
|
Lists may be constructed in several ways:
|
|
|
|
* Using a pair of square brackets to denote the empty list: ``[]``
|
|
* Using square brackets, separating items with commas: ``[a]``, ``[a, b, c]``
|
|
* Using a list comprehension: ``[x for x in iterable]``
|
|
* Using the type constructor: ``list()`` or ``list(iterable)``
|
|
|
|
The constructor builds a list whose items are the same and in the same
|
|
order as *iterable*'s items. *iterable* may be either a sequence, a
|
|
container that supports iteration, or an iterator object. If *iterable*
|
|
is already a list, a copy is made and returned, similar to ``iterable[:]``.
|
|
For example, ``list('abc')`` returns ``['a', 'b', 'c']`` and
|
|
``list( (1, 2, 3) )`` returns ``[1, 2, 3]``.
|
|
If no argument is given, the constructor creates a new empty list, ``[]``.
|
|
|
|
|
|
Many other operations also produce lists, including the :func:`sorted`
|
|
built-in.
|
|
|
|
Lists implement all of the :ref:`common <typesseq-common>` and
|
|
:ref:`mutable <typesseq-mutable>` sequence operations. Lists also provide the
|
|
following additional method:
|
|
|
|
.. method:: list.sort(*, key=None, reverse=None)
|
|
|
|
This method sorts the list in place, using only ``<`` comparisons
|
|
between items. Exceptions are not suppressed - if any comparison operations
|
|
fail, the entire sort operation will fail (and the list will likely be left
|
|
in a partially modified state).
|
|
|
|
:meth:`sort` accepts two arguments that can only be passed by keyword
|
|
(:ref:`keyword-only arguments <keyword-only_parameter>`):
|
|
|
|
*key* specifies a function of one argument that is used to extract a
|
|
comparison key from each list element (for example, ``key=str.lower``).
|
|
The key corresponding to each item in the list is calculated once and
|
|
then used for the entire sorting process. The default value of ``None``
|
|
means that list items are sorted directly without calculating a separate
|
|
key value.
|
|
|
|
The :func:`functools.cmp_to_key` utility is available to convert a 2.x
|
|
style *cmp* function to a *key* function.
|
|
|
|
*reverse* is a boolean value. If set to ``True``, then the list elements
|
|
are sorted as if each comparison were reversed.
|
|
|
|
This method modifies the sequence in place for economy of space when
|
|
sorting a large sequence. To remind users that it operates by side
|
|
effect, it does not return the sorted sequence (use :func:`sorted` to
|
|
explicitly request a new sorted list instance).
|
|
|
|
The :meth:`sort` method is guaranteed to be stable. A sort is stable if it
|
|
guarantees not to change the relative order of elements that compare equal
|
|
--- this is helpful for sorting in multiple passes (for example, sort by
|
|
department, then by salary grade).
|
|
|
|
.. impl-detail::
|
|
|
|
While a list is being sorted, the effect of attempting to mutate, or even
|
|
inspect, the list is undefined. The C implementation of Python makes the
|
|
list appear empty for the duration, and raises :exc:`ValueError` if it can
|
|
detect that the list has been mutated during a sort.
|
|
|
|
|
|
.. _typesseq-tuple:
|
|
|
|
Tuples
|
|
------
|
|
|
|
.. index:: object: tuple
|
|
|
|
Tuples are immutable sequences, typically used to store collections of
|
|
heterogeneous data (such as the 2-tuples produced by the :func:`enumerate`
|
|
built-in). Tuples are also used for cases where an immutable sequence of
|
|
homogeneous data is needed (such as allowing storage in a :class:`set` or
|
|
:class:`dict` instance).
|
|
|
|
.. class:: tuple([iterable])
|
|
|
|
Tuples may be constructed in a number of ways:
|
|
|
|
* Using a pair of parentheses to denote the empty tuple: ``()``
|
|
* Using a trailing comma for a singleton tuple: ``a,`` or ``(a,)``
|
|
* Separating items with commas: ``a, b, c`` or ``(a, b, c)``
|
|
* Using the :func:`tuple` built-in: ``tuple()`` or ``tuple(iterable)``
|
|
|
|
The constructor builds a tuple whose items are the same and in the same
|
|
order as *iterable*'s items. *iterable* may be either a sequence, a
|
|
container that supports iteration, or an iterator object. If *iterable*
|
|
is already a tuple, it is returned unchanged. For example,
|
|
``tuple('abc')`` returns ``('a', 'b', 'c')`` and
|
|
``tuple( [1, 2, 3] )`` returns ``(1, 2, 3)``.
|
|
If no argument is given, the constructor creates a new empty tuple, ``()``.
|
|
|
|
Note that it is actually the comma which makes a tuple, not the parentheses.
|
|
The parentheses are optional, except in the empty tuple case, or
|
|
when they are needed to avoid syntactic ambiguity. For example,
|
|
``f(a, b, c)`` is a function call with three arguments, while
|
|
``f((a, b, c))`` is a function call with a 3-tuple as the sole argument.
|
|
|
|
Tuples implement all of the :ref:`common <typesseq-common>` sequence
|
|
operations.
|
|
|
|
For heterogeneous collections of data where access by name is clearer than
|
|
access by index, :func:`collections.namedtuple` may be a more appropriate
|
|
choice than a simple tuple object.
|
|
|
|
|
|
.. _typesseq-range:
|
|
|
|
Ranges
|
|
------
|
|
|
|
.. index:: object: range
|
|
|
|
The :class:`range` type represents an immutable sequence of numbers and is
|
|
commonly used for looping a specific number of times in :keyword:`for`
|
|
loops.
|
|
|
|
.. class:: range(stop)
|
|
range(start, stop[, step])
|
|
|
|
The arguments to the range constructor must be integers (either built-in
|
|
:class:`int` or any object that implements the ``__index__`` special
|
|
method). If the *step* argument is omitted, it defaults to ``1``.
|
|
If the *start* argument is omitted, it defaults to ``0``.
|
|
If *step* is zero, :exc:`ValueError` is raised.
|
|
|
|
For a positive *step*, the contents of a range ``r`` are determined by the
|
|
formula ``r[i] = start + step*i`` where ``i >= 0`` and
|
|
``r[i] < stop``.
|
|
|
|
For a negative *step*, the contents of the range are still determined by
|
|
the formula ``r[i] = start + step*i``, but the constraints are ``i >= 0``
|
|
and ``r[i] > stop``.
|
|
|
|
A range object will be empty if ``r[0]`` does not meet the value
|
|
constraint. Ranges do support negative indices, but these are interpreted
|
|
as indexing from the end of the sequence determined by the positive
|
|
indices.
|
|
|
|
Ranges containing absolute values larger than :data:`sys.maxsize` are
|
|
permitted but some features (such as :func:`len`) may raise
|
|
:exc:`OverflowError`.
|
|
|
|
Range examples::
|
|
|
|
>>> list(range(10))
|
|
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
|
|
>>> list(range(1, 11))
|
|
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
|
|
>>> list(range(0, 30, 5))
|
|
[0, 5, 10, 15, 20, 25]
|
|
>>> list(range(0, 10, 3))
|
|
[0, 3, 6, 9]
|
|
>>> list(range(0, -10, -1))
|
|
[0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
|
|
>>> list(range(0))
|
|
[]
|
|
>>> list(range(1, 0))
|
|
[]
|
|
|
|
Ranges implement all of the :ref:`common <typesseq-common>` sequence operations
|
|
except concatenation and repetition (due to the fact that range objects can
|
|
only represent sequences that follow a strict pattern and repetition and
|
|
concatenation will usually violate that pattern).
|
|
|
|
.. data: start
|
|
|
|
The value of the *start* parameter (or ``0`` if the parameter was
|
|
not supplied)
|
|
|
|
.. data: stop
|
|
|
|
The value of the *stop* parameter
|
|
|
|
.. data: step
|
|
|
|
The value of the *step* parameter (or ``1`` if the parameter was
|
|
not supplied)
|
|
|
|
The advantage of the :class:`range` type over a regular :class:`list` or
|
|
:class:`tuple` is that a :class:`range` object will always take the same
|
|
(small) amount of memory, no matter the size of the range it represents (as it
|
|
only stores the ``start``, ``stop`` and ``step`` values, calculating individual
|
|
items and subranges as needed).
|
|
|
|
Range objects implement the :class:`collections.abc.Sequence` ABC, and provide
|
|
features such as containment tests, element index lookup, slicing and
|
|
support for negative indices (see :ref:`typesseq`):
|
|
|
|
>>> r = range(0, 20, 2)
|
|
>>> r
|
|
range(0, 20, 2)
|
|
>>> 11 in r
|
|
False
|
|
>>> 10 in r
|
|
True
|
|
>>> r.index(10)
|
|
5
|
|
>>> r[5]
|
|
10
|
|
>>> r[:5]
|
|
range(0, 10, 2)
|
|
>>> r[-1]
|
|
18
|
|
|
|
Testing range objects for equality with ``==`` and ``!=`` compares
|
|
them as sequences. That is, two range objects are considered equal if
|
|
they represent the same sequence of values. (Note that two range
|
|
objects that compare equal might have different :attr:`~range.start`,
|
|
:attr:`~range.stop` and :attr:`~range.step` attributes, for example
|
|
``range(0) == range(2, 1, 3)`` or ``range(0, 3, 2) == range(0, 4, 2)``.)
|
|
|
|
.. versionchanged:: 3.2
|
|
Implement the Sequence ABC.
|
|
Support slicing and negative indices.
|
|
Test :class:`int` objects for membership in constant time instead of
|
|
iterating through all items.
|
|
|
|
.. versionchanged:: 3.3
|
|
Define '==' and '!=' to compare range objects based on the
|
|
sequence of values they define (instead of comparing based on
|
|
object identity).
|
|
|
|
.. versionadded:: 3.3
|
|
The :attr:`~range.start`, :attr:`~range.stop` and :attr:`~range.step`
|
|
attributes.
|
|
|
|
|
|
.. index::
|
|
single: string; text sequence type
|
|
single: str (built-in class); (see also string)
|
|
object: string
|
|
|
|
.. _textseq:
|
|
|
|
Text Sequence Type --- :class:`str`
|
|
===================================
|
|
|
|
Textual data in Python is handled with :class:`str` objects, or :dfn:`strings`.
|
|
Strings are immutable
|
|
:ref:`sequences <typesseq>` of Unicode code points. String literals are
|
|
written in a variety of ways:
|
|
|
|
* Single quotes: ``'allows embedded "double" quotes'``
|
|
* Double quotes: ``"allows embedded 'single' quotes"``.
|
|
* Triple quoted: ``'''Three single quotes'''``, ``"""Three double quotes"""``
|
|
|
|
Triple quoted strings may span multiple lines - all associated whitespace will
|
|
be included in the string literal.
|
|
|
|
String literals that are part of a single expression and have only whitespace
|
|
between them will be implicitly converted to a single string literal. That
|
|
is, ``("spam " "eggs") == "spam eggs"``.
|
|
|
|
See :ref:`strings` for more about the various forms of string literal,
|
|
including supported escape sequences, and the ``r`` ("raw") prefix that
|
|
disables most escape sequence processing.
|
|
|
|
Strings may also be created from other objects using the :class:`str`
|
|
constructor.
|
|
|
|
Since there is no separate "character" type, indexing a string produces
|
|
strings of length 1. That is, for a non-empty string *s*, ``s[0] == s[0:1]``.
|
|
|
|
.. index::
|
|
object: io.StringIO
|
|
|
|
There is also no mutable string type, but :meth:`str.join` or
|
|
:class:`io.StringIO` can be used to efficiently construct strings from
|
|
multiple fragments.
|
|
|
|
.. versionchanged:: 3.3
|
|
For backwards compatibility with the Python 2 series, the ``u`` prefix is
|
|
once again permitted on string literals. It has no effect on the meaning
|
|
of string literals and cannot be combined with the ``r`` prefix.
|
|
|
|
|
|
.. index::
|
|
single: string; str (built-in class)
|
|
|
|
.. class:: str(object='')
|
|
str(object=b'', encoding='utf-8', errors='strict')
|
|
|
|
Return a :ref:`string <textseq>` version of *object*. If *object* is not
|
|
provided, returns the empty string. Otherwise, the behavior of ``str()``
|
|
depends on whether *encoding* or *errors* is given, as follows.
|
|
|
|
If neither *encoding* nor *errors* is given, ``str(object)`` returns
|
|
:meth:`object.__str__() <object.__str__>`, which is the "informal" or nicely
|
|
printable string representation of *object*. For string objects, this is
|
|
the string itself. If *object* does not have a :meth:`~object.__str__`
|
|
method, then :func:`str` falls back to returning
|
|
:meth:`repr(object) <repr>`.
|
|
|
|
.. index::
|
|
single: buffer protocol; str (built-in class)
|
|
single: bytes; str (built-in class)
|
|
|
|
If at least one of *encoding* or *errors* is given, *object* should be a
|
|
:term:`bytes-like object` (e.g. :class:`bytes` or :class:`bytearray`). In
|
|
this case, if *object* is a :class:`bytes` (or :class:`bytearray`) object,
|
|
then ``str(bytes, encoding, errors)`` is equivalent to
|
|
:meth:`bytes.decode(encoding, errors) <bytes.decode>`. Otherwise, the bytes
|
|
object underlying the buffer object is obtained before calling
|
|
:meth:`bytes.decode`. See :ref:`binaryseq` and
|
|
:ref:`bufferobjects` for information on buffer objects.
|
|
|
|
Passing a :class:`bytes` object to :func:`str` without the *encoding*
|
|
or *errors* arguments falls under the first case of returning the informal
|
|
string representation (see also the :option:`-b` command-line option to
|
|
Python). For example::
|
|
|
|
>>> str(b'Zoot!')
|
|
"b'Zoot!'"
|
|
|
|
For more information on the ``str`` class and its methods, see
|
|
:ref:`textseq` and the :ref:`string-methods` section below. To output
|
|
formatted strings, see the :ref:`string-formatting` section. In addition,
|
|
see the :ref:`stringservices` section.
|
|
|
|
|
|
.. index::
|
|
pair: string; methods
|
|
|
|
.. _string-methods:
|
|
|
|
String Methods
|
|
--------------
|
|
|
|
.. index::
|
|
module: re
|
|
|
|
Strings implement all of the :ref:`common <typesseq-common>` sequence
|
|
operations, along with the additional methods described below.
|
|
|
|
Strings also support two styles of string formatting, one providing a large
|
|
degree of flexibility and customization (see :meth:`str.format`,
|
|
:ref:`formatstrings` and :ref:`string-formatting`) and the other based on C
|
|
``printf`` style formatting that handles a narrower range of types and is
|
|
slightly harder to use correctly, but is often faster for the cases it can
|
|
handle (:ref:`old-string-formatting`).
|
|
|
|
The :ref:`textservices` section of the standard library covers a number of
|
|
other modules that provide various text related utilities (including regular
|
|
expression support in the :mod:`re` module).
|
|
|
|
.. method:: str.capitalize()
|
|
|
|
Return a copy of the string with its first character capitalized and the
|
|
rest lowercased.
|
|
|
|
|
|
.. method:: str.casefold()
|
|
|
|
Return a casefolded copy of the string. Casefolded strings may be used for
|
|
caseless matching.
|
|
|
|
Casefolding is similar to lowercasing but more aggressive because it is
|
|
intended to remove all case distinctions in a string. For example, the German
|
|
lowercase letter ``'ß'`` is equivalent to ``"ss"``. Since it is already
|
|
lowercase, :meth:`lower` would do nothing to ``'ß'``; :meth:`casefold`
|
|
converts it to ``"ss"``.
|
|
|
|
The casefolding algorithm is described in section 3.13 of the Unicode
|
|
Standard.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
|
|
.. method:: str.center(width[, fillchar])
|
|
|
|
Return centered in a string of length *width*. Padding is done using the
|
|
specified *fillchar* (default is an ASCII space). The original string is
|
|
returned if *width* is less than or equal to ``len(s)``.
|
|
|
|
|
|
|
|
.. method:: str.count(sub[, start[, end]])
|
|
|
|
Return the number of non-overlapping occurrences of substring *sub* in the
|
|
range [*start*, *end*]. Optional arguments *start* and *end* are
|
|
interpreted as in slice notation.
|
|
|
|
|
|
.. method:: str.encode(encoding="utf-8", errors="strict")
|
|
|
|
Return an encoded version of the string as a bytes object. Default encoding
|
|
is ``'utf-8'``. *errors* may be given to set a different error handling scheme.
|
|
The default for *errors* is ``'strict'``, meaning that encoding errors raise
|
|
a :exc:`UnicodeError`. Other possible
|
|
values are ``'ignore'``, ``'replace'``, ``'xmlcharrefreplace'``,
|
|
``'backslashreplace'`` and any other name registered via
|
|
:func:`codecs.register_error`, see section :ref:`error-handlers`. For a
|
|
list of possible encodings, see section :ref:`standard-encodings`.
|
|
|
|
.. versionchanged:: 3.1
|
|
Support for keyword arguments added.
|
|
|
|
|
|
.. method:: str.endswith(suffix[, start[, end]])
|
|
|
|
Return ``True`` if the string ends with the specified *suffix*, otherwise return
|
|
``False``. *suffix* can also be a tuple of suffixes to look for. With optional
|
|
*start*, test beginning at that position. With optional *end*, stop comparing
|
|
at that position.
|
|
|
|
|
|
.. method:: str.expandtabs(tabsize=8)
|
|
|
|
Return a copy of the string where all tab characters are replaced by one or
|
|
more spaces, depending on the current column and the given tab size. Tab
|
|
positions occur every *tabsize* characters (default is 8, giving tab
|
|
positions at columns 0, 8, 16 and so on). To expand the string, the current
|
|
column is set to zero and the string is examined character by character. If
|
|
the character is a tab (``\t``), one or more space characters are inserted
|
|
in the result until the current column is equal to the next tab position.
|
|
(The tab character itself is not copied.) If the character is a newline
|
|
(``\n``) or return (``\r``), it is copied and the current column is reset to
|
|
zero. Any other character is copied unchanged and the current column is
|
|
incremented by one regardless of how the character is represented when
|
|
printed.
|
|
|
|
>>> '01\t012\t0123\t01234'.expandtabs()
|
|
'01 012 0123 01234'
|
|
>>> '01\t012\t0123\t01234'.expandtabs(4)
|
|
'01 012 0123 01234'
|
|
|
|
|
|
.. method:: str.find(sub[, start[, end]])
|
|
|
|
Return the lowest index in the string where substring *sub* is found, such
|
|
that *sub* is contained in the slice ``s[start:end]``. Optional arguments
|
|
*start* and *end* are interpreted as in slice notation. Return ``-1`` if
|
|
*sub* is not found.
|
|
|
|
.. note::
|
|
|
|
The :meth:`~str.find` method should be used only if you need to know the
|
|
position of *sub*. To check if *sub* is a substring or not, use the
|
|
:keyword:`in` operator::
|
|
|
|
>>> 'Py' in 'Python'
|
|
True
|
|
|
|
|
|
.. method:: str.format(*args, **kwargs)
|
|
|
|
Perform a string formatting operation. The string on which this method is
|
|
called can contain literal text or replacement fields delimited by braces
|
|
``{}``. Each replacement field contains either the numeric index of a
|
|
positional argument, or the name of a keyword argument. Returns a copy of
|
|
the string where each replacement field is replaced with the string value of
|
|
the corresponding argument.
|
|
|
|
>>> "The sum of 1 + 2 is {0}".format(1+2)
|
|
'The sum of 1 + 2 is 3'
|
|
|
|
See :ref:`formatstrings` for a description of the various formatting options
|
|
that can be specified in format strings.
|
|
|
|
|
|
.. method:: str.format_map(mapping)
|
|
|
|
Similar to ``str.format(**mapping)``, except that ``mapping`` is
|
|
used directly and not copied to a :class:`dict`. This is useful
|
|
if for example ``mapping`` is a dict subclass:
|
|
|
|
>>> class Default(dict):
|
|
... def __missing__(self, key):
|
|
... return key
|
|
...
|
|
>>> '{name} was born in {country}'.format_map(Default(name='Guido'))
|
|
'Guido was born in country'
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. method:: str.index(sub[, start[, end]])
|
|
|
|
Like :meth:`~str.find`, but raise :exc:`ValueError` when the substring is
|
|
not found.
|
|
|
|
|
|
.. method:: str.isalnum()
|
|
|
|
Return true if all characters in the string are alphanumeric and there is at
|
|
least one character, false otherwise. A character ``c`` is alphanumeric if one
|
|
of the following returns ``True``: ``c.isalpha()``, ``c.isdecimal()``,
|
|
``c.isdigit()``, or ``c.isnumeric()``.
|
|
|
|
|
|
.. method:: str.isalpha()
|
|
|
|
Return true if all characters in the string are alphabetic and there is at least
|
|
one character, false otherwise. Alphabetic characters are those characters defined
|
|
in the Unicode character database as "Letter", i.e., those with general category
|
|
property being one of "Lm", "Lt", "Lu", "Ll", or "Lo". Note that this is different
|
|
from the "Alphabetic" property defined in the Unicode Standard.
|
|
|
|
|
|
.. method:: str.isdecimal()
|
|
|
|
Return true if all characters in the string are decimal
|
|
characters and there is at least one character, false
|
|
otherwise. Decimal characters are those from general category "Nd". This category
|
|
includes digit characters, and all characters
|
|
that can be used to form decimal-radix numbers, e.g. U+0660,
|
|
ARABIC-INDIC DIGIT ZERO.
|
|
|
|
|
|
.. method:: str.isdigit()
|
|
|
|
Return true if all characters in the string are digits and there is at least one
|
|
character, false otherwise. Digits include decimal characters and digits that need
|
|
special handling, such as the compatibility superscript digits. Formally, a digit
|
|
is a character that has the property value Numeric_Type=Digit or Numeric_Type=Decimal.
|
|
|
|
|
|
.. method:: str.isidentifier()
|
|
|
|
Return true if the string is a valid identifier according to the language
|
|
definition, section :ref:`identifiers`.
|
|
|
|
Use :func:`keyword.iskeyword` to test for reserved identifiers such as
|
|
:keyword:`def` and :keyword:`class`.
|
|
|
|
.. method:: str.islower()
|
|
|
|
Return true if all cased characters [4]_ in the string are lowercase and
|
|
there is at least one cased character, false otherwise.
|
|
|
|
|
|
.. method:: str.isnumeric()
|
|
|
|
Return true if all characters in the string are numeric
|
|
characters, and there is at least one character, false
|
|
otherwise. Numeric characters include digit characters, and all characters
|
|
that have the Unicode numeric value property, e.g. U+2155,
|
|
VULGAR FRACTION ONE FIFTH. Formally, numeric characters are those with the property
|
|
value Numeric_Type=Digit, Numeric_Type=Decimal or Numeric_Type=Numeric.
|
|
|
|
|
|
.. method:: str.isprintable()
|
|
|
|
Return true if all characters in the string are printable or the string is
|
|
empty, false otherwise. Nonprintable characters are those characters defined
|
|
in the Unicode character database as "Other" or "Separator", excepting the
|
|
ASCII space (0x20) which is considered printable. (Note that printable
|
|
characters in this context are those which should not be escaped when
|
|
:func:`repr` is invoked on a string. It has no bearing on the handling of
|
|
strings written to :data:`sys.stdout` or :data:`sys.stderr`.)
|
|
|
|
|
|
.. method:: str.isspace()
|
|
|
|
Return true if there are only whitespace characters in the string and there is
|
|
at least one character, false otherwise. Whitespace characters are those
|
|
characters defined in the Unicode character database as "Other" or "Separator"
|
|
and those with bidirectional property being one of "WS", "B", or "S".
|
|
|
|
.. method:: str.istitle()
|
|
|
|
Return true if the string is a titlecased string and there is at least one
|
|
character, for example uppercase characters may only follow uncased characters
|
|
and lowercase characters only cased ones. Return false otherwise.
|
|
|
|
|
|
.. method:: str.isupper()
|
|
|
|
Return true if all cased characters [4]_ in the string are uppercase and
|
|
there is at least one cased character, false otherwise.
|
|
|
|
|
|
.. method:: str.join(iterable)
|
|
|
|
Return a string which is the concatenation of the strings in the
|
|
:term:`iterable` *iterable*. A :exc:`TypeError` will be raised if there are
|
|
any non-string values in *iterable*, including :class:`bytes` objects. The
|
|
separator between elements is the string providing this method.
|
|
|
|
|
|
.. method:: str.ljust(width[, fillchar])
|
|
|
|
Return the string left justified in a string of length *width*. Padding is
|
|
done using the specified *fillchar* (default is an ASCII space). The
|
|
original string is returned if *width* is less than or equal to ``len(s)``.
|
|
|
|
|
|
.. method:: str.lower()
|
|
|
|
Return a copy of the string with all the cased characters [4]_ converted to
|
|
lowercase.
|
|
|
|
The lowercasing algorithm used is described in section 3.13 of the Unicode
|
|
Standard.
|
|
|
|
|
|
.. method:: str.lstrip([chars])
|
|
|
|
Return a copy of the string with leading characters removed. The *chars*
|
|
argument is a string specifying the set of characters to be removed. If omitted
|
|
or ``None``, the *chars* argument defaults to removing whitespace. The *chars*
|
|
argument is not a prefix; rather, all combinations of its values are stripped::
|
|
|
|
>>> ' spacious '.lstrip()
|
|
'spacious '
|
|
>>> 'www.example.com'.lstrip('cmowz.')
|
|
'example.com'
|
|
|
|
|
|
.. staticmethod:: str.maketrans(x[, y[, z]])
|
|
|
|
This static method returns a translation table usable for :meth:`str.translate`.
|
|
|
|
If there is only one argument, it must be a dictionary mapping Unicode
|
|
ordinals (integers) or characters (strings of length 1) to Unicode ordinals,
|
|
strings (of arbitrary lengths) or None. Character keys will then be
|
|
converted to ordinals.
|
|
|
|
If there are two arguments, they must be strings of equal length, and in the
|
|
resulting dictionary, each character in x will be mapped to the character at
|
|
the same position in y. If there is a third argument, it must be a string,
|
|
whose characters will be mapped to None in the result.
|
|
|
|
|
|
.. method:: str.partition(sep)
|
|
|
|
Split the string at the first occurrence of *sep*, and return a 3-tuple
|
|
containing the part before the separator, the separator itself, and the part
|
|
after the separator. If the separator is not found, return a 3-tuple containing
|
|
the string itself, followed by two empty strings.
|
|
|
|
|
|
.. method:: str.replace(old, new[, count])
|
|
|
|
Return a copy of the string with all occurrences of substring *old* replaced by
|
|
*new*. If the optional argument *count* is given, only the first *count*
|
|
occurrences are replaced.
|
|
|
|
|
|
.. method:: str.rfind(sub[, start[, end]])
|
|
|
|
Return the highest index in the string where substring *sub* is found, such
|
|
that *sub* is contained within ``s[start:end]``. Optional arguments *start*
|
|
and *end* are interpreted as in slice notation. Return ``-1`` on failure.
|
|
|
|
|
|
.. method:: str.rindex(sub[, start[, end]])
|
|
|
|
Like :meth:`rfind` but raises :exc:`ValueError` when the substring *sub* is not
|
|
found.
|
|
|
|
|
|
.. method:: str.rjust(width[, fillchar])
|
|
|
|
Return the string right justified in a string of length *width*. Padding is
|
|
done using the specified *fillchar* (default is an ASCII space). The
|
|
original string is returned if *width* is less than or equal to ``len(s)``.
|
|
|
|
|
|
.. method:: str.rpartition(sep)
|
|
|
|
Split the string at the last occurrence of *sep*, and return a 3-tuple
|
|
containing the part before the separator, the separator itself, and the part
|
|
after the separator. If the separator is not found, return a 3-tuple containing
|
|
two empty strings, followed by the string itself.
|
|
|
|
|
|
.. method:: str.rsplit(sep=None, maxsplit=-1)
|
|
|
|
Return a list of the words in the string, using *sep* as the delimiter string.
|
|
If *maxsplit* is given, at most *maxsplit* splits are done, the *rightmost*
|
|
ones. If *sep* is not specified or ``None``, any whitespace string is a
|
|
separator. Except for splitting from the right, :meth:`rsplit` behaves like
|
|
:meth:`split` which is described in detail below.
|
|
|
|
|
|
.. method:: str.rstrip([chars])
|
|
|
|
Return a copy of the string with trailing characters removed. The *chars*
|
|
argument is a string specifying the set of characters to be removed. If omitted
|
|
or ``None``, the *chars* argument defaults to removing whitespace. The *chars*
|
|
argument is not a suffix; rather, all combinations of its values are stripped::
|
|
|
|
>>> ' spacious '.rstrip()
|
|
' spacious'
|
|
>>> 'mississippi'.rstrip('ipz')
|
|
'mississ'
|
|
|
|
|
|
.. method:: str.split(sep=None, maxsplit=-1)
|
|
|
|
Return a list of the words in the string, using *sep* as the delimiter
|
|
string. If *maxsplit* is given, at most *maxsplit* splits are done (thus,
|
|
the list will have at most ``maxsplit+1`` elements). If *maxsplit* is not
|
|
specified or ``-1``, then there is no limit on the number of splits
|
|
(all possible splits are made).
|
|
|
|
If *sep* is given, consecutive delimiters are not grouped together and are
|
|
deemed to delimit empty strings (for example, ``'1,,2'.split(',')`` returns
|
|
``['1', '', '2']``). The *sep* argument may consist of multiple characters
|
|
(for example, ``'1<>2<>3'.split('<>')`` returns ``['1', '2', '3']``).
|
|
Splitting an empty string with a specified separator returns ``['']``.
|
|
|
|
For example::
|
|
|
|
>>> '1,2,3'.split(',')
|
|
['1', '2', '3']
|
|
>>> '1,2,3'.split(',', maxsplit=1)
|
|
['1', '2,3']
|
|
>>> '1,2,,3,'.split(',')
|
|
['1', '2', '', '3', '']
|
|
|
|
If *sep* is not specified or is ``None``, a different splitting algorithm is
|
|
applied: runs of consecutive whitespace are regarded as a single separator,
|
|
and the result will contain no empty strings at the start or end if the
|
|
string has leading or trailing whitespace. Consequently, splitting an empty
|
|
string or a string consisting of just whitespace with a ``None`` separator
|
|
returns ``[]``.
|
|
|
|
For example::
|
|
|
|
>>> '1 2 3'.split()
|
|
['1', '2', '3']
|
|
>>> '1 2 3'.split(maxsplit=1)
|
|
['1', '2 3']
|
|
>>> ' 1 2 3 '.split()
|
|
['1', '2', '3']
|
|
|
|
|
|
.. index::
|
|
single: universal newlines; str.splitlines method
|
|
|
|
.. method:: str.splitlines([keepends])
|
|
|
|
Return a list of the lines in the string, breaking at line boundaries. Line
|
|
breaks are not included in the resulting list unless *keepends* is given and
|
|
true.
|
|
|
|
This method splits on the following line boundaries. In particular, the
|
|
boundaries are a superset of :term:`universal newlines`.
|
|
|
|
+-----------------------+-----------------------------+
|
|
| Representation | Description |
|
|
+=======================+=============================+
|
|
| ``\n`` | Line Feed |
|
|
+-----------------------+-----------------------------+
|
|
| ``\r`` | Carriage Return |
|
|
+-----------------------+-----------------------------+
|
|
| ``\r\n`` | Carriage Return + Line Feed |
|
|
+-----------------------+-----------------------------+
|
|
| ``\v`` or ``\x0b`` | Line Tabulation |
|
|
+-----------------------+-----------------------------+
|
|
| ``\f`` or ``\x0c`` | Form Feed |
|
|
+-----------------------+-----------------------------+
|
|
| ``\x1c`` | File Separator |
|
|
+-----------------------+-----------------------------+
|
|
| ``\x1d`` | Group Separator |
|
|
+-----------------------+-----------------------------+
|
|
| ``\x1e`` | Record Separator |
|
|
+-----------------------+-----------------------------+
|
|
| ``\x85`` | Next Line (C1 Control Code) |
|
|
+-----------------------+-----------------------------+
|
|
| ``\u2028`` | Line Separator |
|
|
+-----------------------+-----------------------------+
|
|
| ``\u2029`` | Paragraph Separator |
|
|
+-----------------------+-----------------------------+
|
|
|
|
.. versionchanged:: 3.2
|
|
|
|
``\v`` and ``\f`` added to list of line boundaries.
|
|
|
|
For example::
|
|
|
|
>>> 'ab c\n\nde fg\rkl\r\n'.splitlines()
|
|
['ab c', '', 'de fg', 'kl']
|
|
>>> 'ab c\n\nde fg\rkl\r\n'.splitlines(keepends=True)
|
|
['ab c\n', '\n', 'de fg\r', 'kl\r\n']
|
|
|
|
Unlike :meth:`~str.split` when a delimiter string *sep* is given, this
|
|
method returns an empty list for the empty string, and a terminal line
|
|
break does not result in an extra line::
|
|
|
|
>>> "".splitlines()
|
|
[]
|
|
>>> "One line\n".splitlines()
|
|
['One line']
|
|
|
|
For comparison, ``split('\n')`` gives::
|
|
|
|
>>> ''.split('\n')
|
|
['']
|
|
>>> 'Two lines\n'.split('\n')
|
|
['Two lines', '']
|
|
|
|
|
|
.. method:: str.startswith(prefix[, start[, end]])
|
|
|
|
Return ``True`` if string starts with the *prefix*, otherwise return ``False``.
|
|
*prefix* can also be a tuple of prefixes to look for. With optional *start*,
|
|
test string beginning at that position. With optional *end*, stop comparing
|
|
string at that position.
|
|
|
|
|
|
.. method:: str.strip([chars])
|
|
|
|
Return a copy of the string with the leading and trailing characters removed.
|
|
The *chars* argument is a string specifying the set of characters to be removed.
|
|
If omitted or ``None``, the *chars* argument defaults to removing whitespace.
|
|
The *chars* argument is not a prefix or suffix; rather, all combinations of its
|
|
values are stripped::
|
|
|
|
>>> ' spacious '.strip()
|
|
'spacious'
|
|
>>> 'www.example.com'.strip('cmowz.')
|
|
'example'
|
|
|
|
The outermost leading and trailing *chars* argument values are stripped
|
|
from the string. Characters are removed from the leading end until
|
|
reaching a string character that is not contained in the set of
|
|
characters in *chars*. A similar action takes place on the trailing end.
|
|
For example::
|
|
|
|
>>> comment_string = '#....... Section 3.2.1 Issue #32 .......'
|
|
>>> comment_string.strip('.#! ')
|
|
'Section 3.2.1 Issue #32'
|
|
|
|
|
|
.. method:: str.swapcase()
|
|
|
|
Return a copy of the string with uppercase characters converted to lowercase and
|
|
vice versa. Note that it is not necessarily true that
|
|
``s.swapcase().swapcase() == s``.
|
|
|
|
|
|
.. method:: str.title()
|
|
|
|
Return a titlecased version of the string where words start with an uppercase
|
|
character and the remaining characters are lowercase.
|
|
|
|
For example::
|
|
|
|
>>> 'Hello world'.title()
|
|
'Hello World'
|
|
|
|
The algorithm uses a simple language-independent definition of a word as
|
|
groups of consecutive letters. The definition works in many contexts but
|
|
it means that apostrophes in contractions and possessives form word
|
|
boundaries, which may not be the desired result::
|
|
|
|
>>> "they're bill's friends from the UK".title()
|
|
"They'Re Bill'S Friends From The Uk"
|
|
|
|
A workaround for apostrophes can be constructed using regular expressions::
|
|
|
|
>>> import re
|
|
>>> def titlecase(s):
|
|
... return re.sub(r"[A-Za-z]+('[A-Za-z]+)?",
|
|
... lambda mo: mo.group(0)[0].upper() +
|
|
... mo.group(0)[1:].lower(),
|
|
... s)
|
|
...
|
|
>>> titlecase("they're bill's friends.")
|
|
"They're Bill's Friends."
|
|
|
|
|
|
.. method:: str.translate(table)
|
|
|
|
Return a copy of the string in which each character has been mapped through
|
|
the given translation table. The table must be an object that implements
|
|
indexing via :meth:`__getitem__`, typically a :term:`mapping` or
|
|
:term:`sequence`. When indexed by a Unicode ordinal (an integer), the
|
|
table object can do any of the following: return a Unicode ordinal or a
|
|
string, to map the character to one or more other characters; return
|
|
``None``, to delete the character from the return string; or raise a
|
|
:exc:`LookupError` exception, to map the character to itself.
|
|
|
|
You can use :meth:`str.maketrans` to create a translation map from
|
|
character-to-character mappings in different formats.
|
|
|
|
See also the :mod:`codecs` module for a more flexible approach to custom
|
|
character mappings.
|
|
|
|
|
|
.. method:: str.upper()
|
|
|
|
Return a copy of the string with all the cased characters [4]_ converted to
|
|
uppercase. Note that ``str.upper().isupper()`` might be ``False`` if ``s``
|
|
contains uncased characters or if the Unicode category of the resulting
|
|
character(s) is not "Lu" (Letter, uppercase), but e.g. "Lt" (Letter,
|
|
titlecase).
|
|
|
|
The uppercasing algorithm used is described in section 3.13 of the Unicode
|
|
Standard.
|
|
|
|
|
|
.. method:: str.zfill(width)
|
|
|
|
Return a copy of the string left filled with ASCII ``'0'`` digits to
|
|
make a string of length *width*. A leading sign prefix (``'+'``/``'-'``)
|
|
is handled by inserting the padding *after* the sign character rather
|
|
than before. The original string is returned if *width* is less than
|
|
or equal to ``len(s)``.
|
|
|
|
For example::
|
|
|
|
>>> "42".zfill(5)
|
|
'00042'
|
|
>>> "-42".zfill(5)
|
|
'-0042'
|
|
|
|
|
|
|
|
.. _old-string-formatting:
|
|
|
|
``printf``-style String Formatting
|
|
----------------------------------
|
|
|
|
.. index::
|
|
single: formatting, string (%)
|
|
single: interpolation, string (%)
|
|
single: string; formatting
|
|
single: string; interpolation
|
|
single: printf-style formatting
|
|
single: sprintf-style formatting
|
|
single: % formatting
|
|
single: % interpolation
|
|
|
|
.. note::
|
|
|
|
The formatting operations described here exhibit a variety of quirks that
|
|
lead to a number of common errors (such as failing to display tuples and
|
|
dictionaries correctly). Using the newer :meth:`str.format` interface
|
|
helps avoid these errors, and also provides a generally more powerful,
|
|
flexible and extensible approach to formatting text.
|
|
|
|
String objects have one unique built-in operation: the ``%`` operator (modulo).
|
|
This is also known as the string *formatting* or *interpolation* operator.
|
|
Given ``format % values`` (where *format* is a string), ``%`` conversion
|
|
specifications in *format* are replaced with zero or more elements of *values*.
|
|
The effect is similar to using the :c:func:`sprintf` in the C language.
|
|
|
|
If *format* requires a single argument, *values* may be a single non-tuple
|
|
object. [5]_ Otherwise, *values* must be a tuple with exactly the number of
|
|
items specified by the format string, or a single mapping object (for example, a
|
|
dictionary).
|
|
|
|
A conversion specifier contains two or more characters and has the following
|
|
components, which must occur in this order:
|
|
|
|
#. The ``'%'`` character, which marks the start of the specifier.
|
|
|
|
#. Mapping key (optional), consisting of a parenthesised sequence of characters
|
|
(for example, ``(somename)``).
|
|
|
|
#. Conversion flags (optional), which affect the result of some conversion
|
|
types.
|
|
|
|
#. Minimum field width (optional). If specified as an ``'*'`` (asterisk), the
|
|
actual width is read from the next element of the tuple in *values*, and the
|
|
object to convert comes after the minimum field width and optional precision.
|
|
|
|
#. Precision (optional), given as a ``'.'`` (dot) followed by the precision. If
|
|
specified as ``'*'`` (an asterisk), the actual precision is read from the next
|
|
element of the tuple in *values*, and the value to convert comes after the
|
|
precision.
|
|
|
|
#. Length modifier (optional).
|
|
|
|
#. Conversion type.
|
|
|
|
When the right argument is a dictionary (or other mapping type), then the
|
|
formats in the string *must* include a parenthesised mapping key into that
|
|
dictionary inserted immediately after the ``'%'`` character. The mapping key
|
|
selects the value to be formatted from the mapping. For example:
|
|
|
|
>>> print('%(language)s has %(number)03d quote types.' %
|
|
... {'language': "Python", "number": 2})
|
|
Python has 002 quote types.
|
|
|
|
In this case no ``*`` specifiers may occur in a format (since they require a
|
|
sequential parameter list).
|
|
|
|
The conversion flag characters are:
|
|
|
|
+---------+---------------------------------------------------------------------+
|
|
| Flag | Meaning |
|
|
+=========+=====================================================================+
|
|
| ``'#'`` | The value conversion will use the "alternate form" (where defined |
|
|
| | below). |
|
|
+---------+---------------------------------------------------------------------+
|
|
| ``'0'`` | The conversion will be zero padded for numeric values. |
|
|
+---------+---------------------------------------------------------------------+
|
|
| ``'-'`` | The converted value is left adjusted (overrides the ``'0'`` |
|
|
| | conversion if both are given). |
|
|
+---------+---------------------------------------------------------------------+
|
|
| ``' '`` | (a space) A blank should be left before a positive number (or empty |
|
|
| | string) produced by a signed conversion. |
|
|
+---------+---------------------------------------------------------------------+
|
|
| ``'+'`` | A sign character (``'+'`` or ``'-'``) will precede the conversion |
|
|
| | (overrides a "space" flag). |
|
|
+---------+---------------------------------------------------------------------+
|
|
|
|
A length modifier (``h``, ``l``, or ``L``) may be present, but is ignored as it
|
|
is not necessary for Python -- so e.g. ``%ld`` is identical to ``%d``.
|
|
|
|
The conversion types are:
|
|
|
|
+------------+-----------------------------------------------------+-------+
|
|
| Conversion | Meaning | Notes |
|
|
+============+=====================================================+=======+
|
|
| ``'d'`` | Signed integer decimal. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'i'`` | Signed integer decimal. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'o'`` | Signed octal value. | \(1) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'u'`` | Obsolete type -- it is identical to ``'d'``. | \(7) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'x'`` | Signed hexadecimal (lowercase). | \(2) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'X'`` | Signed hexadecimal (uppercase). | \(2) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'e'`` | Floating point exponential format (lowercase). | \(3) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'E'`` | Floating point exponential format (uppercase). | \(3) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'f'`` | Floating point decimal format. | \(3) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'F'`` | Floating point decimal format. | \(3) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'g'`` | Floating point format. Uses lowercase exponential | \(4) |
|
|
| | format if exponent is less than -4 or not less than | |
|
|
| | precision, decimal format otherwise. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'G'`` | Floating point format. Uses uppercase exponential | \(4) |
|
|
| | format if exponent is less than -4 or not less than | |
|
|
| | precision, decimal format otherwise. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'c'`` | Single character (accepts integer or single | |
|
|
| | character string). | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'r'`` | String (converts any Python object using | \(5) |
|
|
| | :func:`repr`). | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'s'`` | String (converts any Python object using | \(5) |
|
|
| | :func:`str`). | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'a'`` | String (converts any Python object using | \(5) |
|
|
| | :func:`ascii`). | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'%'`` | No argument is converted, results in a ``'%'`` | |
|
|
| | character in the result. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
|
|
Notes:
|
|
|
|
(1)
|
|
The alternate form causes a leading zero (``'0'``) to be inserted between
|
|
left-hand padding and the formatting of the number if the leading character
|
|
of the result is not already a zero.
|
|
|
|
(2)
|
|
The alternate form causes a leading ``'0x'`` or ``'0X'`` (depending on whether
|
|
the ``'x'`` or ``'X'`` format was used) to be inserted between left-hand padding
|
|
and the formatting of the number if the leading character of the result is not
|
|
already a zero.
|
|
|
|
(3)
|
|
The alternate form causes the result to always contain a decimal point, even if
|
|
no digits follow it.
|
|
|
|
The precision determines the number of digits after the decimal point and
|
|
defaults to 6.
|
|
|
|
(4)
|
|
The alternate form causes the result to always contain a decimal point, and
|
|
trailing zeroes are not removed as they would otherwise be.
|
|
|
|
The precision determines the number of significant digits before and after the
|
|
decimal point and defaults to 6.
|
|
|
|
(5)
|
|
If precision is ``N``, the output is truncated to ``N`` characters.
|
|
|
|
|
|
(7)
|
|
See :pep:`237`.
|
|
|
|
Since Python strings have an explicit length, ``%s`` conversions do not assume
|
|
that ``'\0'`` is the end of the string.
|
|
|
|
.. XXX Examples?
|
|
|
|
.. versionchanged:: 3.1
|
|
``%f`` conversions for numbers whose absolute value is over 1e50 are no
|
|
longer replaced by ``%g`` conversions.
|
|
|
|
|
|
.. index::
|
|
single: buffer protocol; binary sequence types
|
|
|
|
.. _binaryseq:
|
|
|
|
Binary Sequence Types --- :class:`bytes`, :class:`bytearray`, :class:`memoryview`
|
|
=================================================================================
|
|
|
|
.. index::
|
|
object: bytes
|
|
object: bytearray
|
|
object: memoryview
|
|
module: array
|
|
|
|
The core built-in types for manipulating binary data are :class:`bytes` and
|
|
:class:`bytearray`. They are supported by :class:`memoryview` which uses
|
|
the :ref:`buffer protocol <bufferobjects>` to access the memory of other
|
|
binary objects without needing to make a copy.
|
|
|
|
The :mod:`array` module supports efficient storage of basic data types like
|
|
32-bit integers and IEEE754 double-precision floating values.
|
|
|
|
.. _typebytes:
|
|
|
|
Bytes
|
|
-----
|
|
|
|
.. index:: object: bytes
|
|
|
|
Bytes objects are immutable sequences of single bytes. Since many major
|
|
binary protocols are based on the ASCII text encoding, bytes objects offer
|
|
several methods that are only valid when working with ASCII compatible
|
|
data and are closely related to string objects in a variety of other ways.
|
|
|
|
Firstly, the syntax for bytes literals is largely the same as that for string
|
|
literals, except that a ``b`` prefix is added:
|
|
|
|
* Single quotes: ``b'still allows embedded "double" quotes'``
|
|
* Double quotes: ``b"still allows embedded 'single' quotes"``.
|
|
* Triple quoted: ``b'''3 single quotes'''``, ``b"""3 double quotes"""``
|
|
|
|
Only ASCII characters are permitted in bytes literals (regardless of the
|
|
declared source code encoding). Any binary values over 127 must be entered
|
|
into bytes literals using the appropriate escape sequence.
|
|
|
|
As with string literals, bytes literals may also use a ``r`` prefix to disable
|
|
processing of escape sequences. See :ref:`strings` for more about the various
|
|
forms of bytes literal, including supported escape sequences.
|
|
|
|
While bytes literals and representations are based on ASCII text, bytes
|
|
objects actually behave like immutable sequences of integers, with each
|
|
value in the sequence restricted such that ``0 <= x < 256`` (attempts to
|
|
violate this restriction will trigger :exc:`ValueError`. This is done
|
|
deliberately to emphasise that while many binary formats include ASCII based
|
|
elements and can be usefully manipulated with some text-oriented algorithms,
|
|
this is not generally the case for arbitrary binary data (blindly applying
|
|
text processing algorithms to binary data formats that are not ASCII
|
|
compatible will usually lead to data corruption).
|
|
|
|
In addition to the literal forms, bytes objects can be created in a number of
|
|
other ways:
|
|
|
|
* A zero-filled bytes object of a specified length: ``bytes(10)``
|
|
* From an iterable of integers: ``bytes(range(20))``
|
|
* Copying existing binary data via the buffer protocol: ``bytes(obj)``
|
|
|
|
Also see the :ref:`bytes <func-bytes>` built-in.
|
|
|
|
Since 2 hexadecimal digits correspond precisely to a single byte, hexadecimal
|
|
numbers are a commonly used format for describing binary data. Accordingly,
|
|
the bytes type has an additional class method to read data in that format:
|
|
|
|
.. classmethod:: bytes.fromhex(string)
|
|
|
|
This :class:`bytes` class method returns a bytes object, decoding the
|
|
given string object. The string must contain two hexadecimal digits per
|
|
byte, with ASCII spaces being ignored.
|
|
|
|
>>> bytes.fromhex('2Ef0 F1f2 ')
|
|
b'.\xf0\xf1\xf2'
|
|
|
|
A reverse conversion function exists to transform a bytes object into its
|
|
hexadecimal representation.
|
|
|
|
.. method:: bytes.hex()
|
|
|
|
Return a string object containing two hexadecimal digits for each
|
|
byte in the instance.
|
|
|
|
>>> b'\xf0\xf1\xf2'.hex()
|
|
'f0f1f2'
|
|
|
|
.. versionadded:: 3.5
|
|
|
|
Since bytes objects are sequences of integers (akin to a tuple), for a bytes
|
|
object *b*, ``b[0]`` will be an integer, while ``b[0:1]`` will be a bytes
|
|
object of length 1. (This contrasts with text strings, where both indexing
|
|
and slicing will produce a string of length 1)
|
|
|
|
The representation of bytes objects uses the literal format (``b'...'``)
|
|
since it is often more useful than e.g. ``bytes([46, 46, 46])``. You can
|
|
always convert a bytes object into a list of integers using ``list(b)``.
|
|
|
|
.. note::
|
|
For Python 2.x users: In the Python 2.x series, a variety of implicit
|
|
conversions between 8-bit strings (the closest thing 2.x offers to a
|
|
built-in binary data type) and Unicode strings were permitted. This was a
|
|
backwards compatibility workaround to account for the fact that Python
|
|
originally only supported 8-bit text, and Unicode text was a later
|
|
addition. In Python 3.x, those implicit conversions are gone - conversions
|
|
between 8-bit binary data and Unicode text must be explicit, and bytes and
|
|
string objects will always compare unequal.
|
|
|
|
|
|
.. _typebytearray:
|
|
|
|
Bytearray Objects
|
|
-----------------
|
|
|
|
.. index:: object: bytearray
|
|
|
|
:class:`bytearray` objects are a mutable counterpart to :class:`bytes`
|
|
objects. There is no dedicated literal syntax for bytearray objects, instead
|
|
they are always created by calling the constructor:
|
|
|
|
* Creating an empty instance: ``bytearray()``
|
|
* Creating a zero-filled instance with a given length: ``bytearray(10)``
|
|
* From an iterable of integers: ``bytearray(range(20))``
|
|
* Copying existing binary data via the buffer protocol: ``bytearray(b'Hi!')``
|
|
|
|
As bytearray objects are mutable, they support the
|
|
:ref:`mutable <typesseq-mutable>` sequence operations in addition to the
|
|
common bytes and bytearray operations described in :ref:`bytes-methods`.
|
|
|
|
Also see the :ref:`bytearray <func-bytearray>` built-in.
|
|
|
|
Since 2 hexadecimal digits correspond precisely to a single byte, hexadecimal
|
|
numbers are a commonly used format for describing binary data. Accordingly,
|
|
the bytearray type has an additional class method to read data in that format:
|
|
|
|
.. classmethod:: bytearray.fromhex(string)
|
|
|
|
This :class:`bytearray` class method returns bytearray object, decoding
|
|
the given string object. The string must contain two hexadecimal digits
|
|
per byte, with ASCII spaces being ignored.
|
|
|
|
>>> bytearray.fromhex('2Ef0 F1f2 ')
|
|
bytearray(b'.\xf0\xf1\xf2')
|
|
|
|
A reverse conversion function exists to transform a bytearray object into its
|
|
hexadecimal representation.
|
|
|
|
.. method:: bytearray.hex()
|
|
|
|
Return a string object containing two hexadecimal digits for each
|
|
byte in the instance.
|
|
|
|
>>> bytearray(b'\xf0\xf1\xf2').hex()
|
|
'f0f1f2'
|
|
|
|
.. versionadded:: 3.5
|
|
|
|
Since bytearray objects are sequences of integers (akin to a list), for a
|
|
bytearray object *b*, ``b[0]`` will be an integer, while ``b[0:1]`` will be
|
|
a bytearray object of length 1. (This contrasts with text strings, where
|
|
both indexing and slicing will produce a string of length 1)
|
|
|
|
The representation of bytearray objects uses the bytes literal format
|
|
(``bytearray(b'...')``) since it is often more useful than e.g.
|
|
``bytearray([46, 46, 46])``. You can always convert a bytearray object into
|
|
a list of integers using ``list(b)``.
|
|
|
|
|
|
.. _bytes-methods:
|
|
|
|
Bytes and Bytearray Operations
|
|
------------------------------
|
|
|
|
.. index:: pair: bytes; methods
|
|
pair: bytearray; methods
|
|
|
|
Both bytes and bytearray objects support the :ref:`common <typesseq-common>`
|
|
sequence operations. They interoperate not just with operands of the same
|
|
type, but with any :term:`bytes-like object`. Due to this flexibility, they can be
|
|
freely mixed in operations without causing errors. However, the return type
|
|
of the result may depend on the order of operands.
|
|
|
|
.. note::
|
|
|
|
The methods on bytes and bytearray objects don't accept strings as their
|
|
arguments, just as the methods on strings don't accept bytes as their
|
|
arguments. For example, you have to write::
|
|
|
|
a = "abc"
|
|
b = a.replace("a", "f")
|
|
|
|
and::
|
|
|
|
a = b"abc"
|
|
b = a.replace(b"a", b"f")
|
|
|
|
Some bytes and bytearray operations assume the use of ASCII compatible
|
|
binary formats, and hence should be avoided when working with arbitrary
|
|
binary data. These restrictions are covered below.
|
|
|
|
.. note::
|
|
Using these ASCII based operations to manipulate binary data that is not
|
|
stored in an ASCII based format may lead to data corruption.
|
|
|
|
The following methods on bytes and bytearray objects can be used with
|
|
arbitrary binary data.
|
|
|
|
.. method:: bytes.count(sub[, start[, end]])
|
|
bytearray.count(sub[, start[, end]])
|
|
|
|
Return the number of non-overlapping occurrences of subsequence *sub* in
|
|
the range [*start*, *end*]. Optional arguments *start* and *end* are
|
|
interpreted as in slice notation.
|
|
|
|
The subsequence to search for may be any :term:`bytes-like object` or an
|
|
integer in the range 0 to 255.
|
|
|
|
.. versionchanged:: 3.3
|
|
Also accept an integer in the range 0 to 255 as the subsequence.
|
|
|
|
|
|
.. method:: bytes.decode(encoding="utf-8", errors="strict")
|
|
bytearray.decode(encoding="utf-8", errors="strict")
|
|
|
|
Return a string decoded from the given bytes. Default encoding is
|
|
``'utf-8'``. *errors* may be given to set a different
|
|
error handling scheme. The default for *errors* is ``'strict'``, meaning
|
|
that encoding errors raise a :exc:`UnicodeError`. Other possible values are
|
|
``'ignore'``, ``'replace'`` and any other name registered via
|
|
:func:`codecs.register_error`, see section :ref:`error-handlers`. For a
|
|
list of possible encodings, see section :ref:`standard-encodings`.
|
|
|
|
.. note::
|
|
|
|
Passing the *encoding* argument to :class:`str` allows decoding any
|
|
:term:`bytes-like object` directly, without needing to make a temporary
|
|
bytes or bytearray object.
|
|
|
|
.. versionchanged:: 3.1
|
|
Added support for keyword arguments.
|
|
|
|
|
|
.. method:: bytes.endswith(suffix[, start[, end]])
|
|
bytearray.endswith(suffix[, start[, end]])
|
|
|
|
Return ``True`` if the binary data ends with the specified *suffix*,
|
|
otherwise return ``False``. *suffix* can also be a tuple of suffixes to
|
|
look for. With optional *start*, test beginning at that position. With
|
|
optional *end*, stop comparing at that position.
|
|
|
|
The suffix(es) to search for may be any :term:`bytes-like object`.
|
|
|
|
|
|
.. method:: bytes.find(sub[, start[, end]])
|
|
bytearray.find(sub[, start[, end]])
|
|
|
|
Return the lowest index in the data where the subsequence *sub* is found,
|
|
such that *sub* is contained in the slice ``s[start:end]``. Optional
|
|
arguments *start* and *end* are interpreted as in slice notation. Return
|
|
``-1`` if *sub* is not found.
|
|
|
|
The subsequence to search for may be any :term:`bytes-like object` or an
|
|
integer in the range 0 to 255.
|
|
|
|
.. note::
|
|
|
|
The :meth:`~bytes.find` method should be used only if you need to know the
|
|
position of *sub*. To check if *sub* is a substring or not, use the
|
|
:keyword:`in` operator::
|
|
|
|
>>> b'Py' in b'Python'
|
|
True
|
|
|
|
.. versionchanged:: 3.3
|
|
Also accept an integer in the range 0 to 255 as the subsequence.
|
|
|
|
|
|
.. method:: bytes.index(sub[, start[, end]])
|
|
bytearray.index(sub[, start[, end]])
|
|
|
|
Like :meth:`~bytes.find`, but raise :exc:`ValueError` when the
|
|
subsequence is not found.
|
|
|
|
The subsequence to search for may be any :term:`bytes-like object` or an
|
|
integer in the range 0 to 255.
|
|
|
|
.. versionchanged:: 3.3
|
|
Also accept an integer in the range 0 to 255 as the subsequence.
|
|
|
|
|
|
.. method:: bytes.join(iterable)
|
|
bytearray.join(iterable)
|
|
|
|
Return a bytes or bytearray object which is the concatenation of the
|
|
binary data sequences in the :term:`iterable` *iterable*. A
|
|
:exc:`TypeError` will be raised if there are any values in *iterable*
|
|
that are not :term:`bytes-like objects <bytes-like object>`, including
|
|
:class:`str` objects. The separator between elements is the contents
|
|
of the bytes or bytearray object providing this method.
|
|
|
|
|
|
.. staticmethod:: bytes.maketrans(from, to)
|
|
bytearray.maketrans(from, to)
|
|
|
|
This static method returns a translation table usable for
|
|
:meth:`bytes.translate` that will map each character in *from* into the
|
|
character at the same position in *to*; *from* and *to* must both be
|
|
:term:`bytes-like objects <bytes-like object>` and have the same length.
|
|
|
|
.. versionadded:: 3.1
|
|
|
|
|
|
.. method:: bytes.partition(sep)
|
|
bytearray.partition(sep)
|
|
|
|
Split the sequence at the first occurrence of *sep*, and return a 3-tuple
|
|
containing the part before the separator, the separator, and the part
|
|
after the separator. If the separator is not found, return a 3-tuple
|
|
containing a copy of the original sequence, followed by two empty bytes or
|
|
bytearray objects.
|
|
|
|
The separator to search for may be any :term:`bytes-like object`.
|
|
|
|
|
|
.. method:: bytes.replace(old, new[, count])
|
|
bytearray.replace(old, new[, count])
|
|
|
|
Return a copy of the sequence with all occurrences of subsequence *old*
|
|
replaced by *new*. If the optional argument *count* is given, only the
|
|
first *count* occurrences are replaced.
|
|
|
|
The subsequence to search for and its replacement may be any
|
|
:term:`bytes-like object`.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place - it
|
|
always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.rfind(sub[, start[, end]])
|
|
bytearray.rfind(sub[, start[, end]])
|
|
|
|
Return the highest index in the sequence where the subsequence *sub* is
|
|
found, such that *sub* is contained within ``s[start:end]``. Optional
|
|
arguments *start* and *end* are interpreted as in slice notation. Return
|
|
``-1`` on failure.
|
|
|
|
The subsequence to search for may be any :term:`bytes-like object` or an
|
|
integer in the range 0 to 255.
|
|
|
|
.. versionchanged:: 3.3
|
|
Also accept an integer in the range 0 to 255 as the subsequence.
|
|
|
|
|
|
.. method:: bytes.rindex(sub[, start[, end]])
|
|
bytearray.rindex(sub[, start[, end]])
|
|
|
|
Like :meth:`~bytes.rfind` but raises :exc:`ValueError` when the
|
|
subsequence *sub* is not found.
|
|
|
|
The subsequence to search for may be any :term:`bytes-like object` or an
|
|
integer in the range 0 to 255.
|
|
|
|
.. versionchanged:: 3.3
|
|
Also accept an integer in the range 0 to 255 as the subsequence.
|
|
|
|
|
|
.. method:: bytes.rpartition(sep)
|
|
bytearray.rpartition(sep)
|
|
|
|
Split the sequence at the last occurrence of *sep*, and return a 3-tuple
|
|
containing the part before the separator, the separator, and the part
|
|
after the separator. If the separator is not found, return a 3-tuple
|
|
containing a copy of the original sequence, followed by two empty bytes or
|
|
bytearray objects.
|
|
|
|
The separator to search for may be any :term:`bytes-like object`.
|
|
|
|
|
|
.. method:: bytes.startswith(prefix[, start[, end]])
|
|
bytearray.startswith(prefix[, start[, end]])
|
|
|
|
Return ``True`` if the binary data starts with the specified *prefix*,
|
|
otherwise return ``False``. *prefix* can also be a tuple of prefixes to
|
|
look for. With optional *start*, test beginning at that position. With
|
|
optional *end*, stop comparing at that position.
|
|
|
|
The prefix(es) to search for may be any :term:`bytes-like object`.
|
|
|
|
|
|
.. method:: bytes.translate(table[, delete])
|
|
bytearray.translate(table[, delete])
|
|
|
|
Return a copy of the bytes or bytearray object where all bytes occurring in
|
|
the optional argument *delete* are removed, and the remaining bytes have
|
|
been mapped through the given translation table, which must be a bytes
|
|
object of length 256.
|
|
|
|
You can use the :func:`bytes.maketrans` method to create a translation
|
|
table.
|
|
|
|
Set the *table* argument to ``None`` for translations that only delete
|
|
characters::
|
|
|
|
>>> b'read this short text'.translate(None, b'aeiou')
|
|
b'rd ths shrt txt'
|
|
|
|
|
|
The following methods on bytes and bytearray objects have default behaviours
|
|
that assume the use of ASCII compatible binary formats, but can still be used
|
|
with arbitrary binary data by passing appropriate arguments. Note that all of
|
|
the bytearray methods in this section do *not* operate in place, and instead
|
|
produce new objects.
|
|
|
|
.. method:: bytes.center(width[, fillbyte])
|
|
bytearray.center(width[, fillbyte])
|
|
|
|
Return a copy of the object centered in a sequence of length *width*.
|
|
Padding is done using the specified *fillbyte* (default is an ASCII
|
|
space). For :class:`bytes` objects, the original sequence is returned if
|
|
*width* is less than or equal to ``len(s)``.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place -
|
|
it always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.ljust(width[, fillbyte])
|
|
bytearray.ljust(width[, fillbyte])
|
|
|
|
Return a copy of the object left justified in a sequence of length *width*.
|
|
Padding is done using the specified *fillbyte* (default is an ASCII
|
|
space). For :class:`bytes` objects, the original sequence is returned if
|
|
*width* is less than or equal to ``len(s)``.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place -
|
|
it always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.lstrip([chars])
|
|
bytearray.lstrip([chars])
|
|
|
|
Return a copy of the sequence with specified leading bytes removed. The
|
|
*chars* argument is a binary sequence specifying the set of byte values to
|
|
be removed - the name refers to the fact this method is usually used with
|
|
ASCII characters. If omitted or ``None``, the *chars* argument defaults
|
|
to removing ASCII whitespace. The *chars* argument is not a prefix;
|
|
rather, all combinations of its values are stripped::
|
|
|
|
>>> b' spacious '.lstrip()
|
|
b'spacious '
|
|
>>> b'www.example.com'.lstrip(b'cmowz.')
|
|
b'example.com'
|
|
|
|
The binary sequence of byte values to remove may be any
|
|
:term:`bytes-like object`.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place -
|
|
it always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.rjust(width[, fillbyte])
|
|
bytearray.rjust(width[, fillbyte])
|
|
|
|
Return a copy of the object right justified in a sequence of length *width*.
|
|
Padding is done using the specified *fillbyte* (default is an ASCII
|
|
space). For :class:`bytes` objects, the original sequence is returned if
|
|
*width* is less than or equal to ``len(s)``.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place -
|
|
it always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.rsplit(sep=None, maxsplit=-1)
|
|
bytearray.rsplit(sep=None, maxsplit=-1)
|
|
|
|
Split the binary sequence into subsequences of the same type, using *sep*
|
|
as the delimiter string. If *maxsplit* is given, at most *maxsplit* splits
|
|
are done, the *rightmost* ones. If *sep* is not specified or ``None``,
|
|
any subsequence consisting solely of ASCII whitespace is a separator.
|
|
Except for splitting from the right, :meth:`rsplit` behaves like
|
|
:meth:`split` which is described in detail below.
|
|
|
|
|
|
.. method:: bytes.rstrip([chars])
|
|
bytearray.rstrip([chars])
|
|
|
|
Return a copy of the sequence with specified trailing bytes removed. The
|
|
*chars* argument is a binary sequence specifying the set of byte values to
|
|
be removed - the name refers to the fact this method is usually used with
|
|
ASCII characters. If omitted or ``None``, the *chars* argument defaults to
|
|
removing ASCII whitespace. The *chars* argument is not a suffix; rather,
|
|
all combinations of its values are stripped::
|
|
|
|
>>> b' spacious '.rstrip()
|
|
b' spacious'
|
|
>>> b'mississippi'.rstrip(b'ipz')
|
|
b'mississ'
|
|
|
|
The binary sequence of byte values to remove may be any
|
|
:term:`bytes-like object`.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place -
|
|
it always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.split(sep=None, maxsplit=-1)
|
|
bytearray.split(sep=None, maxsplit=-1)
|
|
|
|
Split the binary sequence into subsequences of the same type, using *sep*
|
|
as the delimiter string. If *maxsplit* is given and non-negative, at most
|
|
*maxsplit* splits are done (thus, the list will have at most ``maxsplit+1``
|
|
elements). If *maxsplit* is not specified or is ``-1``, then there is no
|
|
limit on the number of splits (all possible splits are made).
|
|
|
|
If *sep* is given, consecutive delimiters are not grouped together and are
|
|
deemed to delimit empty subsequences (for example, ``b'1,,2'.split(b',')``
|
|
returns ``[b'1', b'', b'2']``). The *sep* argument may consist of a
|
|
multibyte sequence (for example, ``b'1<>2<>3'.split(b'<>')`` returns
|
|
``[b'1', b'2', b'3']``). Splitting an empty sequence with a specified
|
|
separator returns ``[b'']`` or ``[bytearray(b'')]`` depending on the type
|
|
of object being split. The *sep* argument may be any
|
|
:term:`bytes-like object`.
|
|
|
|
For example::
|
|
|
|
>>> b'1,2,3'.split(b',')
|
|
[b'1', b'2', b'3']
|
|
>>> b'1,2,3'.split(b',', maxsplit=1)
|
|
[b'1', b'2,3']
|
|
>>> b'1,2,,3,'.split(b',')
|
|
[b'1', b'2', b'', b'3', b'']
|
|
|
|
If *sep* is not specified or is ``None``, a different splitting algorithm
|
|
is applied: runs of consecutive ASCII whitespace are regarded as a single
|
|
separator, and the result will contain no empty strings at the start or
|
|
end if the sequence has leading or trailing whitespace. Consequently,
|
|
splitting an empty sequence or a sequence consisting solely of ASCII
|
|
whitespace without a specified separator returns ``[]``.
|
|
|
|
For example::
|
|
|
|
|
|
>>> b'1 2 3'.split()
|
|
[b'1', b'2', b'3']
|
|
>>> b'1 2 3'.split(maxsplit=1)
|
|
[b'1', b'2 3']
|
|
>>> b' 1 2 3 '.split()
|
|
[b'1', b'2', b'3']
|
|
|
|
|
|
.. method:: bytes.strip([chars])
|
|
bytearray.strip([chars])
|
|
|
|
Return a copy of the sequence with specified leading and trailing bytes
|
|
removed. The *chars* argument is a binary sequence specifying the set of
|
|
byte values to be removed - the name refers to the fact this method is
|
|
usually used with ASCII characters. If omitted or ``None``, the *chars*
|
|
argument defaults to removing ASCII whitespace. The *chars* argument is
|
|
not a prefix or suffix; rather, all combinations of its values are
|
|
stripped::
|
|
|
|
>>> b' spacious '.strip()
|
|
b'spacious'
|
|
>>> b'www.example.com'.strip(b'cmowz.')
|
|
b'example'
|
|
|
|
The binary sequence of byte values to remove may be any
|
|
:term:`bytes-like object`.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place -
|
|
it always produces a new object, even if no changes were made.
|
|
|
|
|
|
The following methods on bytes and bytearray objects assume the use of ASCII
|
|
compatible binary formats and should not be applied to arbitrary binary data.
|
|
Note that all of the bytearray methods in this section do *not* operate in
|
|
place, and instead produce new objects.
|
|
|
|
.. method:: bytes.capitalize()
|
|
bytearray.capitalize()
|
|
|
|
Return a copy of the sequence with each byte interpreted as an ASCII
|
|
character, and the first byte capitalized and the rest lowercased.
|
|
Non-ASCII byte values are passed through unchanged.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place - it
|
|
always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.expandtabs(tabsize=8)
|
|
bytearray.expandtabs(tabsize=8)
|
|
|
|
Return a copy of the sequence where all ASCII tab characters are replaced
|
|
by one or more ASCII spaces, depending on the current column and the given
|
|
tab size. Tab positions occur every *tabsize* bytes (default is 8,
|
|
giving tab positions at columns 0, 8, 16 and so on). To expand the
|
|
sequence, the current column is set to zero and the sequence is examined
|
|
byte by byte. If the byte is an ASCII tab character (``b'\t'``), one or
|
|
more space characters are inserted in the result until the current column
|
|
is equal to the next tab position. (The tab character itself is not
|
|
copied.) If the current byte is an ASCII newline (``b'\n'``) or
|
|
carriage return (``b'\r'``), it is copied and the current column is reset
|
|
to zero. Any other byte value is copied unchanged and the current column
|
|
is incremented by one regardless of how the byte value is represented when
|
|
printed::
|
|
|
|
>>> b'01\t012\t0123\t01234'.expandtabs()
|
|
b'01 012 0123 01234'
|
|
>>> b'01\t012\t0123\t01234'.expandtabs(4)
|
|
b'01 012 0123 01234'
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place - it
|
|
always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.isalnum()
|
|
bytearray.isalnum()
|
|
|
|
Return true if all bytes in the sequence are alphabetical ASCII characters
|
|
or ASCII decimal digits and the sequence is not empty, false otherwise.
|
|
Alphabetic ASCII characters are those byte values in the sequence
|
|
``b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'``. ASCII decimal
|
|
digits are those byte values in the sequence ``b'0123456789'``.
|
|
|
|
For example::
|
|
|
|
>>> b'ABCabc1'.isalnum()
|
|
True
|
|
>>> b'ABC abc1'.isalnum()
|
|
False
|
|
|
|
|
|
.. method:: bytes.isalpha()
|
|
bytearray.isalpha()
|
|
|
|
Return true if all bytes in the sequence are alphabetic ASCII characters
|
|
and the sequence is not empty, false otherwise. Alphabetic ASCII
|
|
characters are those byte values in the sequence
|
|
``b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'``.
|
|
|
|
For example::
|
|
|
|
>>> b'ABCabc'.isalpha()
|
|
True
|
|
>>> b'ABCabc1'.isalpha()
|
|
False
|
|
|
|
|
|
.. method:: bytes.isdigit()
|
|
bytearray.isdigit()
|
|
|
|
Return true if all bytes in the sequence are ASCII decimal digits
|
|
and the sequence is not empty, false otherwise. ASCII decimal digits are
|
|
those byte values in the sequence ``b'0123456789'``.
|
|
|
|
For example::
|
|
|
|
>>> b'1234'.isdigit()
|
|
True
|
|
>>> b'1.23'.isdigit()
|
|
False
|
|
|
|
|
|
.. method:: bytes.islower()
|
|
bytearray.islower()
|
|
|
|
Return true if there is at least one lowercase ASCII character
|
|
in the sequence and no uppercase ASCII characters, false otherwise.
|
|
|
|
For example::
|
|
|
|
>>> b'hello world'.islower()
|
|
True
|
|
>>> b'Hello world'.islower()
|
|
False
|
|
|
|
Lowercase ASCII characters are those byte values in the sequence
|
|
``b'abcdefghijklmnopqrstuvwxyz'``. Uppercase ASCII characters
|
|
are those byte values in the sequence ``b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'``.
|
|
|
|
|
|
.. method:: bytes.isspace()
|
|
bytearray.isspace()
|
|
|
|
Return true if all bytes in the sequence are ASCII whitespace and the
|
|
sequence is not empty, false otherwise. ASCII whitespace characters are
|
|
those byte values in the sequence b' \t\n\r\x0b\f' (space, tab, newline,
|
|
carriage return, vertical tab, form feed).
|
|
|
|
|
|
.. method:: bytes.istitle()
|
|
bytearray.istitle()
|
|
|
|
Return true if the sequence is ASCII titlecase and the sequence is not
|
|
empty, false otherwise. See :meth:`bytes.title` for more details on the
|
|
definition of "titlecase".
|
|
|
|
For example::
|
|
|
|
>>> b'Hello World'.istitle()
|
|
True
|
|
>>> b'Hello world'.istitle()
|
|
False
|
|
|
|
|
|
.. method:: bytes.isupper()
|
|
bytearray.isupper()
|
|
|
|
Return true if there is at least one uppercase alphabetic ASCII character
|
|
in the sequence and no lowercase ASCII characters, false otherwise.
|
|
|
|
For example::
|
|
|
|
>>> b'HELLO WORLD'.isupper()
|
|
True
|
|
>>> b'Hello world'.isupper()
|
|
False
|
|
|
|
Lowercase ASCII characters are those byte values in the sequence
|
|
``b'abcdefghijklmnopqrstuvwxyz'``. Uppercase ASCII characters
|
|
are those byte values in the sequence ``b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'``.
|
|
|
|
|
|
.. method:: bytes.lower()
|
|
bytearray.lower()
|
|
|
|
Return a copy of the sequence with all the uppercase ASCII characters
|
|
converted to their corresponding lowercase counterpart.
|
|
|
|
For example::
|
|
|
|
>>> b'Hello World'.lower()
|
|
b'hello world'
|
|
|
|
Lowercase ASCII characters are those byte values in the sequence
|
|
``b'abcdefghijklmnopqrstuvwxyz'``. Uppercase ASCII characters
|
|
are those byte values in the sequence ``b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'``.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place - it
|
|
always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. index::
|
|
single: universal newlines; bytes.splitlines method
|
|
single: universal newlines; bytearray.splitlines method
|
|
|
|
.. method:: bytes.splitlines(keepends=False)
|
|
bytearray.splitlines(keepends=False)
|
|
|
|
Return a list of the lines in the binary sequence, breaking at ASCII
|
|
line boundaries. This method uses the :term:`universal newlines` approach
|
|
to splitting lines. Line breaks are not included in the resulting list
|
|
unless *keepends* is given and true.
|
|
|
|
For example::
|
|
|
|
>>> b'ab c\n\nde fg\rkl\r\n'.splitlines()
|
|
[b'ab c', b'', b'de fg', b'kl']
|
|
>>> b'ab c\n\nde fg\rkl\r\n'.splitlines(keepends=True)
|
|
[b'ab c\n', b'\n', b'de fg\r', b'kl\r\n']
|
|
|
|
Unlike :meth:`~bytes.split` when a delimiter string *sep* is given, this
|
|
method returns an empty list for the empty string, and a terminal line
|
|
break does not result in an extra line::
|
|
|
|
>>> b"".split(b'\n'), b"Two lines\n".split(b'\n')
|
|
([b''], [b'Two lines', b''])
|
|
>>> b"".splitlines(), b"One line\n".splitlines()
|
|
([], [b'One line'])
|
|
|
|
|
|
.. method:: bytes.swapcase()
|
|
bytearray.swapcase()
|
|
|
|
Return a copy of the sequence with all the lowercase ASCII characters
|
|
converted to their corresponding uppercase counterpart and vice-versa.
|
|
|
|
For example::
|
|
|
|
>>> b'Hello World'.swapcase()
|
|
b'hELLO wORLD'
|
|
|
|
Lowercase ASCII characters are those byte values in the sequence
|
|
``b'abcdefghijklmnopqrstuvwxyz'``. Uppercase ASCII characters
|
|
are those byte values in the sequence ``b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'``.
|
|
|
|
Unlike :func:`str.swapcase()`, it is always the case that
|
|
``bin.swapcase().swapcase() == bin`` for the binary versions. Case
|
|
conversions are symmetrical in ASCII, even though that is not generally
|
|
true for arbitrary Unicode code points.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place - it
|
|
always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.title()
|
|
bytearray.title()
|
|
|
|
Return a titlecased version of the binary sequence where words start with
|
|
an uppercase ASCII character and the remaining characters are lowercase.
|
|
Uncased byte values are left unmodified.
|
|
|
|
For example::
|
|
|
|
>>> b'Hello world'.title()
|
|
b'Hello World'
|
|
|
|
Lowercase ASCII characters are those byte values in the sequence
|
|
``b'abcdefghijklmnopqrstuvwxyz'``. Uppercase ASCII characters
|
|
are those byte values in the sequence ``b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'``.
|
|
All other byte values are uncased.
|
|
|
|
The algorithm uses a simple language-independent definition of a word as
|
|
groups of consecutive letters. The definition works in many contexts but
|
|
it means that apostrophes in contractions and possessives form word
|
|
boundaries, which may not be the desired result::
|
|
|
|
>>> b"they're bill's friends from the UK".title()
|
|
b"They'Re Bill'S Friends From The Uk"
|
|
|
|
A workaround for apostrophes can be constructed using regular expressions::
|
|
|
|
>>> import re
|
|
>>> def titlecase(s):
|
|
... return re.sub(rb"[A-Za-z]+('[A-Za-z]+)?",
|
|
... lambda mo: mo.group(0)[0:1].upper() +
|
|
... mo.group(0)[1:].lower(),
|
|
... s)
|
|
...
|
|
>>> titlecase(b"they're bill's friends.")
|
|
b"They're Bill's Friends."
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place - it
|
|
always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.upper()
|
|
bytearray.upper()
|
|
|
|
Return a copy of the sequence with all the lowercase ASCII characters
|
|
converted to their corresponding uppercase counterpart.
|
|
|
|
For example::
|
|
|
|
>>> b'Hello World'.upper()
|
|
b'HELLO WORLD'
|
|
|
|
Lowercase ASCII characters are those byte values in the sequence
|
|
``b'abcdefghijklmnopqrstuvwxyz'``. Uppercase ASCII characters
|
|
are those byte values in the sequence ``b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'``.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place - it
|
|
always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. method:: bytes.zfill(width)
|
|
bytearray.zfill(width)
|
|
|
|
Return a copy of the sequence left filled with ASCII ``b'0'`` digits to
|
|
make a sequence of length *width*. A leading sign prefix (``b'+'``/
|
|
``b'-'`` is handled by inserting the padding *after* the sign character
|
|
rather than before. For :class:`bytes` objects, the original sequence is
|
|
returned if *width* is less than or equal to ``len(seq)``.
|
|
|
|
For example::
|
|
|
|
>>> b"42".zfill(5)
|
|
b'00042'
|
|
>>> b"-42".zfill(5)
|
|
b'-0042'
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place - it
|
|
always produces a new object, even if no changes were made.
|
|
|
|
|
|
.. _bytes-formatting:
|
|
|
|
``printf``-style Bytes Formatting
|
|
----------------------------------
|
|
|
|
.. index::
|
|
single: formatting, bytes (%)
|
|
single: formatting, bytearray (%)
|
|
single: interpolation, bytes (%)
|
|
single: interpolation, bytearray (%)
|
|
single: bytes; formatting
|
|
single: bytearray; formatting
|
|
single: bytes; interpolation
|
|
single: bytearray; interpolation
|
|
single: printf-style formatting
|
|
single: sprintf-style formatting
|
|
single: % formatting
|
|
single: % interpolation
|
|
|
|
.. note::
|
|
|
|
The formatting operations described here exhibit a variety of quirks that
|
|
lead to a number of common errors (such as failing to display tuples and
|
|
dictionaries correctly). If the value being printed may be a tuple or
|
|
dictionary, wrap it in a tuple.
|
|
|
|
Bytes objects (``bytes``/``bytearray``) have one unique built-in operation:
|
|
the ``%`` operator (modulo).
|
|
This is also known as the bytes *formatting* or *interpolation* operator.
|
|
Given ``format % values`` (where *format* is a bytes object), ``%`` conversion
|
|
specifications in *format* are replaced with zero or more elements of *values*.
|
|
The effect is similar to using the :c:func:`sprintf` in the C language.
|
|
|
|
If *format* requires a single argument, *values* may be a single non-tuple
|
|
object. [5]_ Otherwise, *values* must be a tuple with exactly the number of
|
|
items specified by the format bytes object, or a single mapping object (for
|
|
example, a dictionary).
|
|
|
|
A conversion specifier contains two or more characters and has the following
|
|
components, which must occur in this order:
|
|
|
|
#. The ``'%'`` character, which marks the start of the specifier.
|
|
|
|
#. Mapping key (optional), consisting of a parenthesised sequence of characters
|
|
(for example, ``(somename)``).
|
|
|
|
#. Conversion flags (optional), which affect the result of some conversion
|
|
types.
|
|
|
|
#. Minimum field width (optional). If specified as an ``'*'`` (asterisk), the
|
|
actual width is read from the next element of the tuple in *values*, and the
|
|
object to convert comes after the minimum field width and optional precision.
|
|
|
|
#. Precision (optional), given as a ``'.'`` (dot) followed by the precision. If
|
|
specified as ``'*'`` (an asterisk), the actual precision is read from the next
|
|
element of the tuple in *values*, and the value to convert comes after the
|
|
precision.
|
|
|
|
#. Length modifier (optional).
|
|
|
|
#. Conversion type.
|
|
|
|
When the right argument is a dictionary (or other mapping type), then the
|
|
formats in the bytes object *must* include a parenthesised mapping key into that
|
|
dictionary inserted immediately after the ``'%'`` character. The mapping key
|
|
selects the value to be formatted from the mapping. For example:
|
|
|
|
>>> print(b'%(language)s has %(number)03d quote types.' %
|
|
... {b'language': b"Python", b"number": 2})
|
|
b'Python has 002 quote types.'
|
|
|
|
In this case no ``*`` specifiers may occur in a format (since they require a
|
|
sequential parameter list).
|
|
|
|
The conversion flag characters are:
|
|
|
|
+---------+---------------------------------------------------------------------+
|
|
| Flag | Meaning |
|
|
+=========+=====================================================================+
|
|
| ``'#'`` | The value conversion will use the "alternate form" (where defined |
|
|
| | below). |
|
|
+---------+---------------------------------------------------------------------+
|
|
| ``'0'`` | The conversion will be zero padded for numeric values. |
|
|
+---------+---------------------------------------------------------------------+
|
|
| ``'-'`` | The converted value is left adjusted (overrides the ``'0'`` |
|
|
| | conversion if both are given). |
|
|
+---------+---------------------------------------------------------------------+
|
|
| ``' '`` | (a space) A blank should be left before a positive number (or empty |
|
|
| | string) produced by a signed conversion. |
|
|
+---------+---------------------------------------------------------------------+
|
|
| ``'+'`` | A sign character (``'+'`` or ``'-'``) will precede the conversion |
|
|
| | (overrides a "space" flag). |
|
|
+---------+---------------------------------------------------------------------+
|
|
|
|
A length modifier (``h``, ``l``, or ``L``) may be present, but is ignored as it
|
|
is not necessary for Python -- so e.g. ``%ld`` is identical to ``%d``.
|
|
|
|
The conversion types are:
|
|
|
|
+------------+-----------------------------------------------------+-------+
|
|
| Conversion | Meaning | Notes |
|
|
+============+=====================================================+=======+
|
|
| ``'d'`` | Signed integer decimal. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'i'`` | Signed integer decimal. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'o'`` | Signed octal value. | \(1) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'u'`` | Obsolete type -- it is identical to ``'d'``. | \(8) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'x'`` | Signed hexadecimal (lowercase). | \(2) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'X'`` | Signed hexadecimal (uppercase). | \(2) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'e'`` | Floating point exponential format (lowercase). | \(3) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'E'`` | Floating point exponential format (uppercase). | \(3) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'f'`` | Floating point decimal format. | \(3) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'F'`` | Floating point decimal format. | \(3) |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'g'`` | Floating point format. Uses lowercase exponential | \(4) |
|
|
| | format if exponent is less than -4 or not less than | |
|
|
| | precision, decimal format otherwise. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'G'`` | Floating point format. Uses uppercase exponential | \(4) |
|
|
| | format if exponent is less than -4 or not less than | |
|
|
| | precision, decimal format otherwise. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'c'`` | Single byte (accepts integer or single | |
|
|
| | byte objects). | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'b'`` | Bytes (any object that follows the | \(5) |
|
|
| | :ref:`buffer protocol <bufferobjects>` or has | |
|
|
| | :meth:`__bytes__`). | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'s'`` | ``'s'`` is an alias for ``'b'`` and should only | \(6) |
|
|
| | be used for Python2/3 code bases. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'a'`` | Bytes (converts any Python object using | \(5) |
|
|
| | ``repr(obj).encode('ascii','backslashreplace)``). | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'r'`` | ``'r'`` is an alias for ``'a'`` and should only | \(7) |
|
|
| | be used for Python2/3 code bases. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
| ``'%'`` | No argument is converted, results in a ``'%'`` | |
|
|
| | character in the result. | |
|
|
+------------+-----------------------------------------------------+-------+
|
|
|
|
Notes:
|
|
|
|
(1)
|
|
The alternate form causes a leading zero (``'0'``) to be inserted between
|
|
left-hand padding and the formatting of the number if the leading character
|
|
of the result is not already a zero.
|
|
|
|
(2)
|
|
The alternate form causes a leading ``'0x'`` or ``'0X'`` (depending on whether
|
|
the ``'x'`` or ``'X'`` format was used) to be inserted between left-hand padding
|
|
and the formatting of the number if the leading character of the result is not
|
|
already a zero.
|
|
|
|
(3)
|
|
The alternate form causes the result to always contain a decimal point, even if
|
|
no digits follow it.
|
|
|
|
The precision determines the number of digits after the decimal point and
|
|
defaults to 6.
|
|
|
|
(4)
|
|
The alternate form causes the result to always contain a decimal point, and
|
|
trailing zeroes are not removed as they would otherwise be.
|
|
|
|
The precision determines the number of significant digits before and after the
|
|
decimal point and defaults to 6.
|
|
|
|
(5)
|
|
If precision is ``N``, the output is truncated to ``N`` characters.
|
|
|
|
(6)
|
|
``b'%s'`` is deprecated, but will not be removed during the 3.x series.
|
|
|
|
(7)
|
|
``b'%r'`` is deprecated, but will not be removed during the 3.x series.
|
|
|
|
(8)
|
|
See :pep:`237`.
|
|
|
|
.. note::
|
|
|
|
The bytearray version of this method does *not* operate in place - it
|
|
always produces a new object, even if no changes were made.
|
|
|
|
.. seealso:: :pep:`461`.
|
|
.. versionadded:: 3.5
|
|
|
|
.. _typememoryview:
|
|
|
|
Memory Views
|
|
------------
|
|
|
|
:class:`memoryview` objects allow Python code to access the internal data
|
|
of an object that supports the :ref:`buffer protocol <bufferobjects>` without
|
|
copying.
|
|
|
|
.. class:: memoryview(obj)
|
|
|
|
Create a :class:`memoryview` that references *obj*. *obj* must support the
|
|
buffer protocol. Built-in objects that support the buffer protocol include
|
|
:class:`bytes` and :class:`bytearray`.
|
|
|
|
A :class:`memoryview` has the notion of an *element*, which is the
|
|
atomic memory unit handled by the originating object *obj*. For many
|
|
simple types such as :class:`bytes` and :class:`bytearray`, an element
|
|
is a single byte, but other types such as :class:`array.array` may have
|
|
bigger elements.
|
|
|
|
``len(view)`` is equal to the length of :class:`~memoryview.tolist`.
|
|
If ``view.ndim = 0``, the length is 1. If ``view.ndim = 1``, the length
|
|
is equal to the number of elements in the view. For higher dimensions,
|
|
the length is equal to the length of the nested list representation of
|
|
the view. The :class:`~memoryview.itemsize` attribute will give you the
|
|
number of bytes in a single element.
|
|
|
|
A :class:`memoryview` supports slicing and indexing to expose its data.
|
|
One-dimensional slicing will result in a subview::
|
|
|
|
>>> v = memoryview(b'abcefg')
|
|
>>> v[1]
|
|
98
|
|
>>> v[-1]
|
|
103
|
|
>>> v[1:4]
|
|
<memory at 0x7f3ddc9f4350>
|
|
>>> bytes(v[1:4])
|
|
b'bce'
|
|
|
|
If :class:`~memoryview.format` is one of the native format specifiers
|
|
from the :mod:`struct` module, indexing with an integer or a tuple of
|
|
integers is also supported and returns a single *element* with
|
|
the correct type. One-dimensional memoryviews can be indexed
|
|
with an integer or a one-integer tuple. Multi-dimensional memoryviews
|
|
can be indexed with tuples of exactly *ndim* integers where *ndim* is
|
|
the number of dimensions. Zero-dimensional memoryviews can be indexed
|
|
with the empty tuple.
|
|
|
|
Here is an example with a non-byte format::
|
|
|
|
>>> import array
|
|
>>> a = array.array('l', [-11111111, 22222222, -33333333, 44444444])
|
|
>>> m = memoryview(a)
|
|
>>> m[0]
|
|
-11111111
|
|
>>> m[-1]
|
|
44444444
|
|
>>> m[::2].tolist()
|
|
[-11111111, -33333333]
|
|
|
|
If the underlying object is writable, the memoryview supports
|
|
one-dimensional slice assignment. Resizing is not allowed::
|
|
|
|
>>> data = bytearray(b'abcefg')
|
|
>>> v = memoryview(data)
|
|
>>> v.readonly
|
|
False
|
|
>>> v[0] = ord(b'z')
|
|
>>> data
|
|
bytearray(b'zbcefg')
|
|
>>> v[1:4] = b'123'
|
|
>>> data
|
|
bytearray(b'z123fg')
|
|
>>> v[2:3] = b'spam'
|
|
Traceback (most recent call last):
|
|
File "<stdin>", line 1, in <module>
|
|
ValueError: memoryview assignment: lvalue and rvalue have different structures
|
|
>>> v[2:6] = b'spam'
|
|
>>> data
|
|
bytearray(b'z1spam')
|
|
|
|
One-dimensional memoryviews of hashable (read-only) types with formats
|
|
'B', 'b' or 'c' are also hashable. The hash is defined as
|
|
``hash(m) == hash(m.tobytes())``::
|
|
|
|
>>> v = memoryview(b'abcefg')
|
|
>>> hash(v) == hash(b'abcefg')
|
|
True
|
|
>>> hash(v[2:4]) == hash(b'ce')
|
|
True
|
|
>>> hash(v[::-2]) == hash(b'abcefg'[::-2])
|
|
True
|
|
|
|
.. versionchanged:: 3.3
|
|
One-dimensional memoryviews can now be sliced.
|
|
One-dimensional memoryviews with formats 'B', 'b' or 'c' are now hashable.
|
|
|
|
.. versionchanged:: 3.4
|
|
memoryview is now registered automatically with
|
|
:class:`collections.abc.Sequence`
|
|
|
|
.. versionchanged:: 3.5
|
|
memoryviews can now be indexed with tuple of integers.
|
|
|
|
:class:`memoryview` has several methods:
|
|
|
|
.. method:: __eq__(exporter)
|
|
|
|
A memoryview and a :pep:`3118` exporter are equal if their shapes are
|
|
equivalent and if all corresponding values are equal when the operands'
|
|
respective format codes are interpreted using :mod:`struct` syntax.
|
|
|
|
For the subset of :mod:`struct` format strings currently supported by
|
|
:meth:`tolist`, ``v`` and ``w`` are equal if ``v.tolist() == w.tolist()``::
|
|
|
|
>>> import array
|
|
>>> a = array.array('I', [1, 2, 3, 4, 5])
|
|
>>> b = array.array('d', [1.0, 2.0, 3.0, 4.0, 5.0])
|
|
>>> c = array.array('b', [5, 3, 1])
|
|
>>> x = memoryview(a)
|
|
>>> y = memoryview(b)
|
|
>>> x == a == y == b
|
|
True
|
|
>>> x.tolist() == a.tolist() == y.tolist() == b.tolist()
|
|
True
|
|
>>> z = y[::-2]
|
|
>>> z == c
|
|
True
|
|
>>> z.tolist() == c.tolist()
|
|
True
|
|
|
|
If either format string is not supported by the :mod:`struct` module,
|
|
then the objects will always compare as unequal (even if the format
|
|
strings and buffer contents are identical)::
|
|
|
|
>>> from ctypes import BigEndianStructure, c_long
|
|
>>> class BEPoint(BigEndianStructure):
|
|
... _fields_ = [("x", c_long), ("y", c_long)]
|
|
...
|
|
>>> point = BEPoint(100, 200)
|
|
>>> a = memoryview(point)
|
|
>>> b = memoryview(point)
|
|
>>> a == point
|
|
False
|
|
>>> a == b
|
|
False
|
|
|
|
Note that, as with floating point numbers, ``v is w`` does *not* imply
|
|
``v == w`` for memoryview objects.
|
|
|
|
.. versionchanged:: 3.3
|
|
Previous versions compared the raw memory disregarding the item format
|
|
and the logical array structure.
|
|
|
|
.. method:: tobytes()
|
|
|
|
Return the data in the buffer as a bytestring. This is equivalent to
|
|
calling the :class:`bytes` constructor on the memoryview. ::
|
|
|
|
>>> m = memoryview(b"abc")
|
|
>>> m.tobytes()
|
|
b'abc'
|
|
>>> bytes(m)
|
|
b'abc'
|
|
|
|
For non-contiguous arrays the result is equal to the flattened list
|
|
representation with all elements converted to bytes. :meth:`tobytes`
|
|
supports all format strings, including those that are not in
|
|
:mod:`struct` module syntax.
|
|
|
|
.. method:: hex()
|
|
|
|
Return a string object containing two hexadecimal digits for each
|
|
byte in the buffer. ::
|
|
|
|
>>> m = memoryview(b"abc")
|
|
>>> m.hex()
|
|
'616263'
|
|
|
|
.. versionadded:: 3.5
|
|
|
|
.. method:: tolist()
|
|
|
|
Return the data in the buffer as a list of elements. ::
|
|
|
|
>>> memoryview(b'abc').tolist()
|
|
[97, 98, 99]
|
|
>>> import array
|
|
>>> a = array.array('d', [1.1, 2.2, 3.3])
|
|
>>> m = memoryview(a)
|
|
>>> m.tolist()
|
|
[1.1, 2.2, 3.3]
|
|
|
|
.. versionchanged:: 3.3
|
|
:meth:`tolist` now supports all single character native formats in
|
|
:mod:`struct` module syntax as well as multi-dimensional
|
|
representations.
|
|
|
|
.. method:: release()
|
|
|
|
Release the underlying buffer exposed by the memoryview object. Many
|
|
objects take special actions when a view is held on them (for example,
|
|
a :class:`bytearray` would temporarily forbid resizing); therefore,
|
|
calling release() is handy to remove these restrictions (and free any
|
|
dangling resources) as soon as possible.
|
|
|
|
After this method has been called, any further operation on the view
|
|
raises a :class:`ValueError` (except :meth:`release()` itself which can
|
|
be called multiple times)::
|
|
|
|
>>> m = memoryview(b'abc')
|
|
>>> m.release()
|
|
>>> m[0]
|
|
Traceback (most recent call last):
|
|
File "<stdin>", line 1, in <module>
|
|
ValueError: operation forbidden on released memoryview object
|
|
|
|
The context management protocol can be used for a similar effect,
|
|
using the ``with`` statement::
|
|
|
|
>>> with memoryview(b'abc') as m:
|
|
... m[0]
|
|
...
|
|
97
|
|
>>> m[0]
|
|
Traceback (most recent call last):
|
|
File "<stdin>", line 1, in <module>
|
|
ValueError: operation forbidden on released memoryview object
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
.. method:: cast(format[, shape])
|
|
|
|
Cast a memoryview to a new format or shape. *shape* defaults to
|
|
``[byte_length//new_itemsize]``, which means that the result view
|
|
will be one-dimensional. The return value is a new memoryview, but
|
|
the buffer itself is not copied. Supported casts are 1D -> C-:term:`contiguous`
|
|
and C-contiguous -> 1D.
|
|
|
|
The destination format is restricted to a single element native format in
|
|
:mod:`struct` syntax. One of the formats must be a byte format
|
|
('B', 'b' or 'c'). The byte length of the result must be the same
|
|
as the original length.
|
|
|
|
Cast 1D/long to 1D/unsigned bytes::
|
|
|
|
>>> import array
|
|
>>> a = array.array('l', [1,2,3])
|
|
>>> x = memoryview(a)
|
|
>>> x.format
|
|
'l'
|
|
>>> x.itemsize
|
|
8
|
|
>>> len(x)
|
|
3
|
|
>>> x.nbytes
|
|
24
|
|
>>> y = x.cast('B')
|
|
>>> y.format
|
|
'B'
|
|
>>> y.itemsize
|
|
1
|
|
>>> len(y)
|
|
24
|
|
>>> y.nbytes
|
|
24
|
|
|
|
Cast 1D/unsigned bytes to 1D/char::
|
|
|
|
>>> b = bytearray(b'zyz')
|
|
>>> x = memoryview(b)
|
|
>>> x[0] = b'a'
|
|
Traceback (most recent call last):
|
|
File "<stdin>", line 1, in <module>
|
|
ValueError: memoryview: invalid value for format "B"
|
|
>>> y = x.cast('c')
|
|
>>> y[0] = b'a'
|
|
>>> b
|
|
bytearray(b'ayz')
|
|
|
|
Cast 1D/bytes to 3D/ints to 1D/signed char::
|
|
|
|
>>> import struct
|
|
>>> buf = struct.pack("i"*12, *list(range(12)))
|
|
>>> x = memoryview(buf)
|
|
>>> y = x.cast('i', shape=[2,2,3])
|
|
>>> y.tolist()
|
|
[[[0, 1, 2], [3, 4, 5]], [[6, 7, 8], [9, 10, 11]]]
|
|
>>> y.format
|
|
'i'
|
|
>>> y.itemsize
|
|
4
|
|
>>> len(y)
|
|
2
|
|
>>> y.nbytes
|
|
48
|
|
>>> z = y.cast('b')
|
|
>>> z.format
|
|
'b'
|
|
>>> z.itemsize
|
|
1
|
|
>>> len(z)
|
|
48
|
|
>>> z.nbytes
|
|
48
|
|
|
|
Cast 1D/unsigned char to 2D/unsigned long::
|
|
|
|
>>> buf = struct.pack("L"*6, *list(range(6)))
|
|
>>> x = memoryview(buf)
|
|
>>> y = x.cast('L', shape=[2,3])
|
|
>>> len(y)
|
|
2
|
|
>>> y.nbytes
|
|
48
|
|
>>> y.tolist()
|
|
[[0, 1, 2], [3, 4, 5]]
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
.. versionchanged:: 3.5
|
|
The source format is no longer restricted when casting to a byte view.
|
|
|
|
There are also several readonly attributes available:
|
|
|
|
.. attribute:: obj
|
|
|
|
The underlying object of the memoryview::
|
|
|
|
>>> b = bytearray(b'xyz')
|
|
>>> m = memoryview(b)
|
|
>>> m.obj is b
|
|
True
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
.. attribute:: nbytes
|
|
|
|
``nbytes == product(shape) * itemsize == len(m.tobytes())``. This is
|
|
the amount of space in bytes that the array would use in a contiguous
|
|
representation. It is not necessarily equal to len(m)::
|
|
|
|
>>> import array
|
|
>>> a = array.array('i', [1,2,3,4,5])
|
|
>>> m = memoryview(a)
|
|
>>> len(m)
|
|
5
|
|
>>> m.nbytes
|
|
20
|
|
>>> y = m[::2]
|
|
>>> len(y)
|
|
3
|
|
>>> y.nbytes
|
|
12
|
|
>>> len(y.tobytes())
|
|
12
|
|
|
|
Multi-dimensional arrays::
|
|
|
|
>>> import struct
|
|
>>> buf = struct.pack("d"*12, *[1.5*x for x in range(12)])
|
|
>>> x = memoryview(buf)
|
|
>>> y = x.cast('d', shape=[3,4])
|
|
>>> y.tolist()
|
|
[[0.0, 1.5, 3.0, 4.5], [6.0, 7.5, 9.0, 10.5], [12.0, 13.5, 15.0, 16.5]]
|
|
>>> len(y)
|
|
3
|
|
>>> y.nbytes
|
|
96
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
.. attribute:: readonly
|
|
|
|
A bool indicating whether the memory is read only.
|
|
|
|
.. attribute:: format
|
|
|
|
A string containing the format (in :mod:`struct` module style) for each
|
|
element in the view. A memoryview can be created from exporters with
|
|
arbitrary format strings, but some methods (e.g. :meth:`tolist`) are
|
|
restricted to native single element formats.
|
|
|
|
.. versionchanged:: 3.3
|
|
format ``'B'`` is now handled according to the struct module syntax.
|
|
This means that ``memoryview(b'abc')[0] == b'abc'[0] == 97``.
|
|
|
|
.. attribute:: itemsize
|
|
|
|
The size in bytes of each element of the memoryview::
|
|
|
|
>>> import array, struct
|
|
>>> m = memoryview(array.array('H', [32000, 32001, 32002]))
|
|
>>> m.itemsize
|
|
2
|
|
>>> m[0]
|
|
32000
|
|
>>> struct.calcsize('H') == m.itemsize
|
|
True
|
|
|
|
.. attribute:: ndim
|
|
|
|
An integer indicating how many dimensions of a multi-dimensional array the
|
|
memory represents.
|
|
|
|
.. attribute:: shape
|
|
|
|
A tuple of integers the length of :attr:`ndim` giving the shape of the
|
|
memory as an N-dimensional array.
|
|
|
|
.. versionchanged:: 3.3
|
|
An empty tuple instead of None when ndim = 0.
|
|
|
|
.. attribute:: strides
|
|
|
|
A tuple of integers the length of :attr:`ndim` giving the size in bytes to
|
|
access each element for each dimension of the array.
|
|
|
|
.. versionchanged:: 3.3
|
|
An empty tuple instead of None when ndim = 0.
|
|
|
|
.. attribute:: suboffsets
|
|
|
|
Used internally for PIL-style arrays. The value is informational only.
|
|
|
|
.. attribute:: c_contiguous
|
|
|
|
A bool indicating whether the memory is C-:term:`contiguous`.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
.. attribute:: f_contiguous
|
|
|
|
A bool indicating whether the memory is Fortran :term:`contiguous`.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
.. attribute:: contiguous
|
|
|
|
A bool indicating whether the memory is :term:`contiguous`.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
|
|
.. _types-set:
|
|
|
|
Set Types --- :class:`set`, :class:`frozenset`
|
|
==============================================
|
|
|
|
.. index:: object: set
|
|
|
|
A :dfn:`set` object is an unordered collection of distinct :term:`hashable` objects.
|
|
Common uses include membership testing, removing duplicates from a sequence, and
|
|
computing mathematical operations such as intersection, union, difference, and
|
|
symmetric difference.
|
|
(For other containers see the built-in :class:`dict`, :class:`list`,
|
|
and :class:`tuple` classes, and the :mod:`collections` module.)
|
|
|
|
Like other collections, sets support ``x in set``, ``len(set)``, and ``for x in
|
|
set``. Being an unordered collection, sets do not record element position or
|
|
order of insertion. Accordingly, sets do not support indexing, slicing, or
|
|
other sequence-like behavior.
|
|
|
|
There are currently two built-in set types, :class:`set` and :class:`frozenset`.
|
|
The :class:`set` type is mutable --- the contents can be changed using methods
|
|
like :meth:`~set.add` and :meth:`~set.remove`. Since it is mutable, it has no
|
|
hash value and cannot be used as either a dictionary key or as an element of
|
|
another set. The :class:`frozenset` type is immutable and :term:`hashable` ---
|
|
its contents cannot be altered after it is created; it can therefore be used as
|
|
a dictionary key or as an element of another set.
|
|
|
|
Non-empty sets (not frozensets) can be created by placing a comma-separated list
|
|
of elements within braces, for example: ``{'jack', 'sjoerd'}``, in addition to the
|
|
:class:`set` constructor.
|
|
|
|
The constructors for both classes work the same:
|
|
|
|
.. class:: set([iterable])
|
|
frozenset([iterable])
|
|
|
|
Return a new set or frozenset object whose elements are taken from
|
|
*iterable*. The elements of a set must be :term:`hashable`. To
|
|
represent sets of sets, the inner sets must be :class:`frozenset`
|
|
objects. If *iterable* is not specified, a new empty set is
|
|
returned.
|
|
|
|
Instances of :class:`set` and :class:`frozenset` provide the following
|
|
operations:
|
|
|
|
.. describe:: len(s)
|
|
|
|
Return the cardinality of set *s*.
|
|
|
|
.. describe:: x in s
|
|
|
|
Test *x* for membership in *s*.
|
|
|
|
.. describe:: x not in s
|
|
|
|
Test *x* for non-membership in *s*.
|
|
|
|
.. method:: isdisjoint(other)
|
|
|
|
Return ``True`` if the set has no elements in common with *other*. Sets are
|
|
disjoint if and only if their intersection is the empty set.
|
|
|
|
.. method:: issubset(other)
|
|
set <= other
|
|
|
|
Test whether every element in the set is in *other*.
|
|
|
|
.. method:: set < other
|
|
|
|
Test whether the set is a proper subset of *other*, that is,
|
|
``set <= other and set != other``.
|
|
|
|
.. method:: issuperset(other)
|
|
set >= other
|
|
|
|
Test whether every element in *other* is in the set.
|
|
|
|
.. method:: set > other
|
|
|
|
Test whether the set is a proper superset of *other*, that is, ``set >=
|
|
other and set != other``.
|
|
|
|
.. method:: union(other, ...)
|
|
set | other | ...
|
|
|
|
Return a new set with elements from the set and all others.
|
|
|
|
.. method:: intersection(other, ...)
|
|
set & other & ...
|
|
|
|
Return a new set with elements common to the set and all others.
|
|
|
|
.. method:: difference(other, ...)
|
|
set - other - ...
|
|
|
|
Return a new set with elements in the set that are not in the others.
|
|
|
|
.. method:: symmetric_difference(other)
|
|
set ^ other
|
|
|
|
Return a new set with elements in either the set or *other* but not both.
|
|
|
|
.. method:: copy()
|
|
|
|
Return a new set with a shallow copy of *s*.
|
|
|
|
|
|
Note, the non-operator versions of :meth:`union`, :meth:`intersection`,
|
|
:meth:`difference`, and :meth:`symmetric_difference`, :meth:`issubset`, and
|
|
:meth:`issuperset` methods will accept any iterable as an argument. In
|
|
contrast, their operator based counterparts require their arguments to be
|
|
sets. This precludes error-prone constructions like ``set('abc') & 'cbs'``
|
|
in favor of the more readable ``set('abc').intersection('cbs')``.
|
|
|
|
Both :class:`set` and :class:`frozenset` support set to set comparisons. Two
|
|
sets are equal if and only if every element of each set is contained in the
|
|
other (each is a subset of the other). A set is less than another set if and
|
|
only if the first set is a proper subset of the second set (is a subset, but
|
|
is not equal). A set is greater than another set if and only if the first set
|
|
is a proper superset of the second set (is a superset, but is not equal).
|
|
|
|
Instances of :class:`set` are compared to instances of :class:`frozenset`
|
|
based on their members. For example, ``set('abc') == frozenset('abc')``
|
|
returns ``True`` and so does ``set('abc') in set([frozenset('abc')])``.
|
|
|
|
The subset and equality comparisons do not generalize to a total ordering
|
|
function. For example, any two nonempty disjoint sets are not equal and are not
|
|
subsets of each other, so *all* of the following return ``False``: ``a<b``,
|
|
``a==b``, or ``a>b``.
|
|
|
|
Since sets only define partial ordering (subset relationships), the output of
|
|
the :meth:`list.sort` method is undefined for lists of sets.
|
|
|
|
Set elements, like dictionary keys, must be :term:`hashable`.
|
|
|
|
Binary operations that mix :class:`set` instances with :class:`frozenset`
|
|
return the type of the first operand. For example: ``frozenset('ab') |
|
|
set('bc')`` returns an instance of :class:`frozenset`.
|
|
|
|
The following table lists operations available for :class:`set` that do not
|
|
apply to immutable instances of :class:`frozenset`:
|
|
|
|
.. method:: update(other, ...)
|
|
set |= other | ...
|
|
|
|
Update the set, adding elements from all others.
|
|
|
|
.. method:: intersection_update(other, ...)
|
|
set &= other & ...
|
|
|
|
Update the set, keeping only elements found in it and all others.
|
|
|
|
.. method:: difference_update(other, ...)
|
|
set -= other | ...
|
|
|
|
Update the set, removing elements found in others.
|
|
|
|
.. method:: symmetric_difference_update(other)
|
|
set ^= other
|
|
|
|
Update the set, keeping only elements found in either set, but not in both.
|
|
|
|
.. method:: add(elem)
|
|
|
|
Add element *elem* to the set.
|
|
|
|
.. method:: remove(elem)
|
|
|
|
Remove element *elem* from the set. Raises :exc:`KeyError` if *elem* is
|
|
not contained in the set.
|
|
|
|
.. method:: discard(elem)
|
|
|
|
Remove element *elem* from the set if it is present.
|
|
|
|
.. method:: pop()
|
|
|
|
Remove and return an arbitrary element from the set. Raises
|
|
:exc:`KeyError` if the set is empty.
|
|
|
|
.. method:: clear()
|
|
|
|
Remove all elements from the set.
|
|
|
|
|
|
Note, the non-operator versions of the :meth:`update`,
|
|
:meth:`intersection_update`, :meth:`difference_update`, and
|
|
:meth:`symmetric_difference_update` methods will accept any iterable as an
|
|
argument.
|
|
|
|
Note, the *elem* argument to the :meth:`__contains__`, :meth:`remove`, and
|
|
:meth:`discard` methods may be a set. To support searching for an equivalent
|
|
frozenset, the *elem* set is temporarily mutated during the search and then
|
|
restored. During the search, the *elem* set should not be read or mutated
|
|
since it does not have a meaningful value.
|
|
|
|
|
|
.. _typesmapping:
|
|
|
|
Mapping Types --- :class:`dict`
|
|
===============================
|
|
|
|
.. index::
|
|
object: mapping
|
|
object: dictionary
|
|
triple: operations on; mapping; types
|
|
triple: operations on; dictionary; type
|
|
statement: del
|
|
builtin: len
|
|
|
|
A :term:`mapping` object maps :term:`hashable` values to arbitrary objects.
|
|
Mappings are mutable objects. There is currently only one standard mapping
|
|
type, the :dfn:`dictionary`. (For other containers see the built-in
|
|
:class:`list`, :class:`set`, and :class:`tuple` classes, and the
|
|
:mod:`collections` module.)
|
|
|
|
A dictionary's keys are *almost* arbitrary values. Values that are not
|
|
:term:`hashable`, that is, values containing lists, dictionaries or other
|
|
mutable types (that are compared by value rather than by object identity) may
|
|
not be used as keys. Numeric types used for keys obey the normal rules for
|
|
numeric comparison: if two numbers compare equal (such as ``1`` and ``1.0``)
|
|
then they can be used interchangeably to index the same dictionary entry. (Note
|
|
however, that since computers store floating-point numbers as approximations it
|
|
is usually unwise to use them as dictionary keys.)
|
|
|
|
Dictionaries can be created by placing a comma-separated list of ``key: value``
|
|
pairs within braces, for example: ``{'jack': 4098, 'sjoerd': 4127}`` or ``{4098:
|
|
'jack', 4127: 'sjoerd'}``, or by the :class:`dict` constructor.
|
|
|
|
.. class:: dict(**kwarg)
|
|
dict(mapping, **kwarg)
|
|
dict(iterable, **kwarg)
|
|
|
|
Return a new dictionary initialized from an optional positional argument
|
|
and a possibly empty set of keyword arguments.
|
|
|
|
If no positional argument is given, an empty dictionary is created.
|
|
If a positional argument is given and it is a mapping object, a dictionary
|
|
is created with the same key-value pairs as the mapping object. Otherwise,
|
|
the positional argument must be an :term:`iterable` object. Each item in
|
|
the iterable must itself be an iterable with exactly two objects. The
|
|
first object of each item becomes a key in the new dictionary, and the
|
|
second object the corresponding value. If a key occurs more than once, the
|
|
last value for that key becomes the corresponding value in the new
|
|
dictionary.
|
|
|
|
If keyword arguments are given, the keyword arguments and their values are
|
|
added to the dictionary created from the positional argument. If a key
|
|
being added is already present, the value from the keyword argument
|
|
replaces the value from the positional argument.
|
|
|
|
To illustrate, the following examples all return a dictionary equal to
|
|
``{"one": 1, "two": 2, "three": 3}``::
|
|
|
|
>>> a = dict(one=1, two=2, three=3)
|
|
>>> b = {'one': 1, 'two': 2, 'three': 3}
|
|
>>> c = dict(zip(['one', 'two', 'three'], [1, 2, 3]))
|
|
>>> d = dict([('two', 2), ('one', 1), ('three', 3)])
|
|
>>> e = dict({'three': 3, 'one': 1, 'two': 2})
|
|
>>> a == b == c == d == e
|
|
True
|
|
|
|
Providing keyword arguments as in the first example only works for keys that
|
|
are valid Python identifiers. Otherwise, any valid keys can be used.
|
|
|
|
|
|
These are the operations that dictionaries support (and therefore, custom
|
|
mapping types should support too):
|
|
|
|
.. describe:: len(d)
|
|
|
|
Return the number of items in the dictionary *d*.
|
|
|
|
.. describe:: d[key]
|
|
|
|
Return the item of *d* with key *key*. Raises a :exc:`KeyError` if *key* is
|
|
not in the map.
|
|
|
|
.. index:: __missing__()
|
|
|
|
If a subclass of dict defines a method :meth:`__missing__` and *key*
|
|
is not present, the ``d[key]`` operation calls that method with the key *key*
|
|
as argument. The ``d[key]`` operation then returns or raises whatever is
|
|
returned or raised by the ``__missing__(key)`` call.
|
|
No other operations or methods invoke :meth:`__missing__`. If
|
|
:meth:`__missing__` is not defined, :exc:`KeyError` is raised.
|
|
:meth:`__missing__` must be a method; it cannot be an instance variable::
|
|
|
|
>>> class Counter(dict):
|
|
... def __missing__(self, key):
|
|
... return 0
|
|
>>> c = Counter()
|
|
>>> c['red']
|
|
0
|
|
>>> c['red'] += 1
|
|
>>> c['red']
|
|
1
|
|
|
|
The example above shows part of the implementation of
|
|
:class:`collections.Counter`. A different ``__missing__`` method is used
|
|
by :class:`collections.defaultdict`.
|
|
|
|
.. describe:: d[key] = value
|
|
|
|
Set ``d[key]`` to *value*.
|
|
|
|
.. describe:: del d[key]
|
|
|
|
Remove ``d[key]`` from *d*. Raises a :exc:`KeyError` if *key* is not in the
|
|
map.
|
|
|
|
.. describe:: key in d
|
|
|
|
Return ``True`` if *d* has a key *key*, else ``False``.
|
|
|
|
.. describe:: key not in d
|
|
|
|
Equivalent to ``not key in d``.
|
|
|
|
.. describe:: iter(d)
|
|
|
|
Return an iterator over the keys of the dictionary. This is a shortcut
|
|
for ``iter(d.keys())``.
|
|
|
|
.. method:: clear()
|
|
|
|
Remove all items from the dictionary.
|
|
|
|
.. method:: copy()
|
|
|
|
Return a shallow copy of the dictionary.
|
|
|
|
.. classmethod:: fromkeys(seq[, value])
|
|
|
|
Create a new dictionary with keys from *seq* and values set to *value*.
|
|
|
|
:meth:`fromkeys` is a class method that returns a new dictionary. *value*
|
|
defaults to ``None``.
|
|
|
|
.. method:: get(key[, default])
|
|
|
|
Return the value for *key* if *key* is in the dictionary, else *default*.
|
|
If *default* is not given, it defaults to ``None``, so that this method
|
|
never raises a :exc:`KeyError`.
|
|
|
|
.. method:: items()
|
|
|
|
Return a new view of the dictionary's items (``(key, value)`` pairs).
|
|
See the :ref:`documentation of view objects <dict-views>`.
|
|
|
|
.. method:: keys()
|
|
|
|
Return a new view of the dictionary's keys. See the :ref:`documentation
|
|
of view objects <dict-views>`.
|
|
|
|
.. method:: pop(key[, default])
|
|
|
|
If *key* is in the dictionary, remove it and return its value, else return
|
|
*default*. If *default* is not given and *key* is not in the dictionary,
|
|
a :exc:`KeyError` is raised.
|
|
|
|
.. method:: popitem()
|
|
|
|
Remove and return an arbitrary ``(key, value)`` pair from the dictionary.
|
|
|
|
:meth:`popitem` is useful to destructively iterate over a dictionary, as
|
|
often used in set algorithms. If the dictionary is empty, calling
|
|
:meth:`popitem` raises a :exc:`KeyError`.
|
|
|
|
.. method:: setdefault(key[, default])
|
|
|
|
If *key* is in the dictionary, return its value. If not, insert *key*
|
|
with a value of *default* and return *default*. *default* defaults to
|
|
``None``.
|
|
|
|
.. method:: update([other])
|
|
|
|
Update the dictionary with the key/value pairs from *other*, overwriting
|
|
existing keys. Return ``None``.
|
|
|
|
:meth:`update` accepts either another dictionary object or an iterable of
|
|
key/value pairs (as tuples or other iterables of length two). If keyword
|
|
arguments are specified, the dictionary is then updated with those
|
|
key/value pairs: ``d.update(red=1, blue=2)``.
|
|
|
|
.. method:: values()
|
|
|
|
Return a new view of the dictionary's values. See the
|
|
:ref:`documentation of view objects <dict-views>`.
|
|
|
|
Dictionaries compare equal if and only if they have the same ``(key,
|
|
value)`` pairs. Order comparisons ('<', '<=', '>=', '>') raise
|
|
:exc:`TypeError`.
|
|
|
|
.. seealso::
|
|
:class:`types.MappingProxyType` can be used to create a read-only view
|
|
of a :class:`dict`.
|
|
|
|
|
|
.. _dict-views:
|
|
|
|
Dictionary view objects
|
|
-----------------------
|
|
|
|
The objects returned by :meth:`dict.keys`, :meth:`dict.values` and
|
|
:meth:`dict.items` are *view objects*. They provide a dynamic view on the
|
|
dictionary's entries, which means that when the dictionary changes, the view
|
|
reflects these changes.
|
|
|
|
Dictionary views can be iterated over to yield their respective data, and
|
|
support membership tests:
|
|
|
|
.. describe:: len(dictview)
|
|
|
|
Return the number of entries in the dictionary.
|
|
|
|
.. describe:: iter(dictview)
|
|
|
|
Return an iterator over the keys, values or items (represented as tuples of
|
|
``(key, value)``) in the dictionary.
|
|
|
|
Keys and values are iterated over in an arbitrary order which is non-random,
|
|
varies across Python implementations, and depends on the dictionary's history
|
|
of insertions and deletions. If keys, values and items views are iterated
|
|
over with no intervening modifications to the dictionary, the order of items
|
|
will directly correspond. This allows the creation of ``(value, key)`` pairs
|
|
using :func:`zip`: ``pairs = zip(d.values(), d.keys())``. Another way to
|
|
create the same list is ``pairs = [(v, k) for (k, v) in d.items()]``.
|
|
|
|
Iterating views while adding or deleting entries in the dictionary may raise
|
|
a :exc:`RuntimeError` or fail to iterate over all entries.
|
|
|
|
.. describe:: x in dictview
|
|
|
|
Return ``True`` if *x* is in the underlying dictionary's keys, values or
|
|
items (in the latter case, *x* should be a ``(key, value)`` tuple).
|
|
|
|
|
|
Keys views are set-like since their entries are unique and hashable. If all
|
|
values are hashable, so that ``(key, value)`` pairs are unique and hashable,
|
|
then the items view is also set-like. (Values views are not treated as set-like
|
|
since the entries are generally not unique.) For set-like views, all of the
|
|
operations defined for the abstract base class :class:`collections.abc.Set` are
|
|
available (for example, ``==``, ``<``, or ``^``).
|
|
|
|
An example of dictionary view usage::
|
|
|
|
>>> dishes = {'eggs': 2, 'sausage': 1, 'bacon': 1, 'spam': 500}
|
|
>>> keys = dishes.keys()
|
|
>>> values = dishes.values()
|
|
|
|
>>> # iteration
|
|
>>> n = 0
|
|
>>> for val in values:
|
|
... n += val
|
|
>>> print(n)
|
|
504
|
|
|
|
>>> # keys and values are iterated over in the same order
|
|
>>> list(keys)
|
|
['eggs', 'bacon', 'sausage', 'spam']
|
|
>>> list(values)
|
|
[2, 1, 1, 500]
|
|
|
|
>>> # view objects are dynamic and reflect dict changes
|
|
>>> del dishes['eggs']
|
|
>>> del dishes['sausage']
|
|
>>> list(keys)
|
|
['spam', 'bacon']
|
|
|
|
>>> # set operations
|
|
>>> keys & {'eggs', 'bacon', 'salad'}
|
|
{'bacon'}
|
|
>>> keys ^ {'sausage', 'juice'}
|
|
{'juice', 'sausage', 'bacon', 'spam'}
|
|
|
|
|
|
.. _typecontextmanager:
|
|
|
|
Context Manager Types
|
|
=====================
|
|
|
|
.. index::
|
|
single: context manager
|
|
single: context management protocol
|
|
single: protocol; context management
|
|
|
|
Python's :keyword:`with` statement supports the concept of a runtime context
|
|
defined by a context manager. This is implemented using a pair of methods
|
|
that allow user-defined classes to define a runtime context that is entered
|
|
before the statement body is executed and exited when the statement ends:
|
|
|
|
|
|
.. method:: contextmanager.__enter__()
|
|
|
|
Enter the runtime context and return either this object or another object
|
|
related to the runtime context. The value returned by this method is bound to
|
|
the identifier in the :keyword:`as` clause of :keyword:`with` statements using
|
|
this context manager.
|
|
|
|
An example of a context manager that returns itself is a :term:`file object`.
|
|
File objects return themselves from __enter__() to allow :func:`open` to be
|
|
used as the context expression in a :keyword:`with` statement.
|
|
|
|
An example of a context manager that returns a related object is the one
|
|
returned by :func:`decimal.localcontext`. These managers set the active
|
|
decimal context to a copy of the original decimal context and then return the
|
|
copy. This allows changes to be made to the current decimal context in the body
|
|
of the :keyword:`with` statement without affecting code outside the
|
|
:keyword:`with` statement.
|
|
|
|
|
|
.. method:: contextmanager.__exit__(exc_type, exc_val, exc_tb)
|
|
|
|
Exit the runtime context and return a Boolean flag indicating if any exception
|
|
that occurred should be suppressed. If an exception occurred while executing the
|
|
body of the :keyword:`with` statement, the arguments contain the exception type,
|
|
value and traceback information. Otherwise, all three arguments are ``None``.
|
|
|
|
Returning a true value from this method will cause the :keyword:`with` statement
|
|
to suppress the exception and continue execution with the statement immediately
|
|
following the :keyword:`with` statement. Otherwise the exception continues
|
|
propagating after this method has finished executing. Exceptions that occur
|
|
during execution of this method will replace any exception that occurred in the
|
|
body of the :keyword:`with` statement.
|
|
|
|
The exception passed in should never be reraised explicitly - instead, this
|
|
method should return a false value to indicate that the method completed
|
|
successfully and does not want to suppress the raised exception. This allows
|
|
context management code to easily detect whether or not an :meth:`__exit__`
|
|
method has actually failed.
|
|
|
|
Python defines several context managers to support easy thread synchronisation,
|
|
prompt closure of files or other objects, and simpler manipulation of the active
|
|
decimal arithmetic context. The specific types are not treated specially beyond
|
|
their implementation of the context management protocol. See the
|
|
:mod:`contextlib` module for some examples.
|
|
|
|
Python's :term:`generator`\s and the :class:`contextlib.contextmanager` decorator
|
|
provide a convenient way to implement these protocols. If a generator function is
|
|
decorated with the :class:`contextlib.contextmanager` decorator, it will return a
|
|
context manager implementing the necessary :meth:`__enter__` and
|
|
:meth:`__exit__` methods, rather than the iterator produced by an undecorated
|
|
generator function.
|
|
|
|
Note that there is no specific slot for any of these methods in the type
|
|
structure for Python objects in the Python/C API. Extension types wanting to
|
|
define these methods must provide them as a normal Python accessible method.
|
|
Compared to the overhead of setting up the runtime context, the overhead of a
|
|
single class dictionary lookup is negligible.
|
|
|
|
|
|
.. _typesother:
|
|
|
|
Other Built-in Types
|
|
====================
|
|
|
|
The interpreter supports several other kinds of objects. Most of these support
|
|
only one or two operations.
|
|
|
|
|
|
.. _typesmodules:
|
|
|
|
Modules
|
|
-------
|
|
|
|
The only special operation on a module is attribute access: ``m.name``, where
|
|
*m* is a module and *name* accesses a name defined in *m*'s symbol table.
|
|
Module attributes can be assigned to. (Note that the :keyword:`import`
|
|
statement is not, strictly speaking, an operation on a module object; ``import
|
|
foo`` does not require a module object named *foo* to exist, rather it requires
|
|
an (external) *definition* for a module named *foo* somewhere.)
|
|
|
|
A special attribute of every module is :attr:`~object.__dict__`. This is the
|
|
dictionary containing the module's symbol table. Modifying this dictionary will
|
|
actually change the module's symbol table, but direct assignment to the
|
|
:attr:`__dict__` attribute is not possible (you can write
|
|
``m.__dict__['a'] = 1``, which defines ``m.a`` to be ``1``, but you can't write
|
|
``m.__dict__ = {}``). Modifying :attr:`__dict__` directly is not recommended.
|
|
|
|
Modules built into the interpreter are written like this: ``<module 'sys'
|
|
(built-in)>``. If loaded from a file, they are written as ``<module 'os' from
|
|
'/usr/local/lib/pythonX.Y/os.pyc'>``.
|
|
|
|
|
|
.. _typesobjects:
|
|
|
|
Classes and Class Instances
|
|
---------------------------
|
|
|
|
See :ref:`objects` and :ref:`class` for these.
|
|
|
|
|
|
.. _typesfunctions:
|
|
|
|
Functions
|
|
---------
|
|
|
|
Function objects are created by function definitions. The only operation on a
|
|
function object is to call it: ``func(argument-list)``.
|
|
|
|
There are really two flavors of function objects: built-in functions and
|
|
user-defined functions. Both support the same operation (to call the function),
|
|
but the implementation is different, hence the different object types.
|
|
|
|
See :ref:`function` for more information.
|
|
|
|
|
|
.. _typesmethods:
|
|
|
|
Methods
|
|
-------
|
|
|
|
.. index:: object: method
|
|
|
|
Methods are functions that are called using the attribute notation. There are
|
|
two flavors: built-in methods (such as :meth:`append` on lists) and class
|
|
instance methods. Built-in methods are described with the types that support
|
|
them.
|
|
|
|
If you access a method (a function defined in a class namespace) through an
|
|
instance, you get a special object: a :dfn:`bound method` (also called
|
|
:dfn:`instance method`) object. When called, it will add the ``self`` argument
|
|
to the argument list. Bound methods have two special read-only attributes:
|
|
``m.__self__`` is the object on which the method operates, and ``m.__func__`` is
|
|
the function implementing the method. Calling ``m(arg-1, arg-2, ..., arg-n)``
|
|
is completely equivalent to calling ``m.__func__(m.__self__, arg-1, arg-2, ...,
|
|
arg-n)``.
|
|
|
|
Like function objects, bound method objects support getting arbitrary
|
|
attributes. However, since method attributes are actually stored on the
|
|
underlying function object (``meth.__func__``), setting method attributes on
|
|
bound methods is disallowed. Attempting to set an attribute on a method
|
|
results in an :exc:`AttributeError` being raised. In order to set a method
|
|
attribute, you need to explicitly set it on the underlying function object::
|
|
|
|
>>> class C:
|
|
... def method(self):
|
|
... pass
|
|
...
|
|
>>> c = C()
|
|
>>> c.method.whoami = 'my name is method' # can't set on the method
|
|
Traceback (most recent call last):
|
|
File "<stdin>", line 1, in <module>
|
|
AttributeError: 'method' object has no attribute 'whoami'
|
|
>>> c.method.__func__.whoami = 'my name is method'
|
|
>>> c.method.whoami
|
|
'my name is method'
|
|
|
|
See :ref:`types` for more information.
|
|
|
|
|
|
.. _bltin-code-objects:
|
|
|
|
Code Objects
|
|
------------
|
|
|
|
.. index:: object: code
|
|
|
|
.. index::
|
|
builtin: compile
|
|
single: __code__ (function object attribute)
|
|
|
|
Code objects are used by the implementation to represent "pseudo-compiled"
|
|
executable Python code such as a function body. They differ from function
|
|
objects because they don't contain a reference to their global execution
|
|
environment. Code objects are returned by the built-in :func:`compile` function
|
|
and can be extracted from function objects through their :attr:`__code__`
|
|
attribute. See also the :mod:`code` module.
|
|
|
|
.. index::
|
|
builtin: exec
|
|
builtin: eval
|
|
|
|
A code object can be executed or evaluated by passing it (instead of a source
|
|
string) to the :func:`exec` or :func:`eval` built-in functions.
|
|
|
|
See :ref:`types` for more information.
|
|
|
|
|
|
.. _bltin-type-objects:
|
|
|
|
Type Objects
|
|
------------
|
|
|
|
.. index::
|
|
builtin: type
|
|
module: types
|
|
|
|
Type objects represent the various object types. An object's type is accessed
|
|
by the built-in function :func:`type`. There are no special operations on
|
|
types. The standard module :mod:`types` defines names for all standard built-in
|
|
types.
|
|
|
|
Types are written like this: ``<class 'int'>``.
|
|
|
|
|
|
.. _bltin-null-object:
|
|
|
|
The Null Object
|
|
---------------
|
|
|
|
This object is returned by functions that don't explicitly return a value. It
|
|
supports no special operations. There is exactly one null object, named
|
|
``None`` (a built-in name). ``type(None)()`` produces the same singleton.
|
|
|
|
It is written as ``None``.
|
|
|
|
|
|
.. _bltin-ellipsis-object:
|
|
|
|
The Ellipsis Object
|
|
-------------------
|
|
|
|
This object is commonly used by slicing (see :ref:`slicings`). It supports no
|
|
special operations. There is exactly one ellipsis object, named
|
|
:const:`Ellipsis` (a built-in name). ``type(Ellipsis)()`` produces the
|
|
:const:`Ellipsis` singleton.
|
|
|
|
It is written as ``Ellipsis`` or ``...``.
|
|
|
|
|
|
.. _bltin-notimplemented-object:
|
|
|
|
The NotImplemented Object
|
|
-------------------------
|
|
|
|
This object is returned from comparisons and binary operations when they are
|
|
asked to operate on types they don't support. See :ref:`comparisons` for more
|
|
information. There is exactly one ``NotImplemented`` object.
|
|
``type(NotImplemented)()`` produces the singleton instance.
|
|
|
|
It is written as ``NotImplemented``.
|
|
|
|
|
|
.. _bltin-boolean-values:
|
|
|
|
Boolean Values
|
|
--------------
|
|
|
|
Boolean values are the two constant objects ``False`` and ``True``. They are
|
|
used to represent truth values (although other values can also be considered
|
|
false or true). In numeric contexts (for example when used as the argument to
|
|
an arithmetic operator), they behave like the integers 0 and 1, respectively.
|
|
The built-in function :func:`bool` can be used to convert any value to a
|
|
Boolean, if the value can be interpreted as a truth value (see section
|
|
:ref:`truth` above).
|
|
|
|
.. index::
|
|
single: False
|
|
single: True
|
|
pair: Boolean; values
|
|
|
|
They are written as ``False`` and ``True``, respectively.
|
|
|
|
|
|
.. _typesinternal:
|
|
|
|
Internal Objects
|
|
----------------
|
|
|
|
See :ref:`types` for this information. It describes stack frame objects,
|
|
traceback objects, and slice objects.
|
|
|
|
|
|
.. _specialattrs:
|
|
|
|
Special Attributes
|
|
==================
|
|
|
|
The implementation adds a few special read-only attributes to several object
|
|
types, where they are relevant. Some of these are not reported by the
|
|
:func:`dir` built-in function.
|
|
|
|
|
|
.. attribute:: object.__dict__
|
|
|
|
A dictionary or other mapping object used to store an object's (writable)
|
|
attributes.
|
|
|
|
|
|
.. attribute:: instance.__class__
|
|
|
|
The class to which a class instance belongs.
|
|
|
|
|
|
.. attribute:: class.__bases__
|
|
|
|
The tuple of base classes of a class object.
|
|
|
|
|
|
.. attribute:: class.__name__
|
|
|
|
The name of the class or type.
|
|
|
|
|
|
.. attribute:: class.__qualname__
|
|
|
|
The :term:`qualified name` of the class or type.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
|
|
.. attribute:: class.__mro__
|
|
|
|
This attribute is a tuple of classes that are considered when looking for
|
|
base classes during method resolution.
|
|
|
|
|
|
.. method:: class.mro()
|
|
|
|
This method can be overridden by a metaclass to customize the method
|
|
resolution order for its instances. It is called at class instantiation, and
|
|
its result is stored in :attr:`~class.__mro__`.
|
|
|
|
|
|
.. method:: class.__subclasses__
|
|
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Each class keeps a list of weak references to its immediate subclasses. This
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method returns a list of all those references still alive.
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Example::
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>>> int.__subclasses__()
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[<class 'bool'>]
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.. rubric:: Footnotes
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.. [1] Additional information on these special methods may be found in the Python
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Reference Manual (:ref:`customization`).
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.. [2] As a consequence, the list ``[1, 2]`` is considered equal to ``[1.0, 2.0]``, and
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similarly for tuples.
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.. [3] They must have since the parser can't tell the type of the operands.
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.. [4] Cased characters are those with general category property being one of
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"Lu" (Letter, uppercase), "Ll" (Letter, lowercase), or "Lt" (Letter, titlecase).
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.. [5] To format only a tuple you should therefore provide a singleton tuple whose only
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element is the tuple to be formatted.
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