2007-08-15 11:28:01 -03:00
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.. 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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.. note::
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Historically (until release 2.2), Python's built-in types have differed from
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user-defined types because it was not possible to use the built-in types as the
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basis for object-oriented inheritance. This limitation no longer
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exists.
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.. index:: pair: built-in; types
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The principal built-in types are numerics, sequences, mappings, files, classes,
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instances and exceptions.
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.. index:: statement: print
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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``, ``0L``, ``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:`__nonzero__`
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or :meth:`__len__` method, when that method returns the integer zero or
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:class:`bool` value ``False``. [#]_
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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:: pair: chaining; comparisons
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Comparison operations are supported by all objects. 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 | Notes |
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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 | \(1) |
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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: operator; comparison
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operator: ==
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2007-12-29 06:57:00 -04:00
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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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2007-08-15 11:28:01 -03:00
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operator: is
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operator: is not
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Notes:
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(1)
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``!=`` can also be written ``<>``, but this is an obsolete usage
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kept for backwards compatibility only. New code should always use
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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 and different string
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types, never compare equal; such objects are ordered consistently but
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arbitrarily (so that sorting a heterogeneous array yields a consistent result).
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Furthermore, some types (for example, file objects) support only a degenerate
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notion of comparison where any two objects of that type are unequal. Again,
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such objects are ordered arbitrarily but consistently. The ``<``, ``<=``, ``>``
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and ``>=`` operators will raise a :exc:`TypeError` exception when any operand is
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a complex number.
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.. index:: single: __cmp__() (instance method)
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Instances of a class normally compare as non-equal unless the class defines the
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:meth:`__cmp__` method. Refer to :ref:`customization`) for information on the
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use of this method to effect object comparisons.
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**Implementation note:** Objects of different types except numbers are ordered
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by their type names; objects of the same types that don't support proper
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comparison are ordered by their address.
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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, ``in`` and ``not in``, are
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supported only by sequence types (below).
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.. _typesnumeric:
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Numeric Types --- :class:`int`, :class:`float`, :class:`long`, :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: long 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 four distinct numeric types: :dfn:`plain integers`, :dfn:`long
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integers`, :dfn:`floating point numbers`, and :dfn:`complex numbers`. In
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addition, Booleans are a subtype of plain integers. Plain integers (also just
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called :dfn:`integers`) are implemented using :ctype:`long` in C, which gives
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them at least 32 bits of precision (``sys.maxint`` is always set to the maximum
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plain integer value for the current platform, the minimum value is
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``-sys.maxint - 1``). Long integers have unlimited precision. Floating point
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numbers are implemented using :ctype:`double` in C. All bets on their precision
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are off unless you happen to know the machine you are working with.
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Complex numbers have a real and imaginary part, which are each implemented using
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:ctype:`double` in C. To extract these parts from a complex number *z*, use
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``z.real`` and ``z.imag``.
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.. index::
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pair: numeric; literals
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pair: integer; literals
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triple: long; 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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Numbers are created by numeric literals or as the result of built-in functions
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2008-10-30 19:44:18 -03:00
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and operators. Unadorned integer literals (including binary, hex, and octal
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numbers) yield plain integers unless the value they denote is too large to be
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represented as a plain integer, in which case they yield a long integer.
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Integer literals with an ``'L'`` or ``'l'`` suffix yield long integers (``'L'``
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is preferred because ``1l`` looks too much like eleven!). Numeric literals
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containing a decimal point or an exponent sign yield floating point numbers.
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Appending ``'j'`` or ``'J'`` to a numeric literal yields a complex number with a
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zero real part. A complex numeric literal is the sum of a real and an imaginary
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part.
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2007-08-15 11:28:01 -03:00
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.. index::
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single: arithmetic
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builtin: int
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builtin: long
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builtin: float
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builtin: complex
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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 plain integer is narrower than long integer
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is narrower than floating point is narrower than complex. Comparisons between
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numbers of mixed type use the same rule. [#]_ The constructors :func:`int`,
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:func:`long`, :func:`float`, and :func:`complex` can be used to produce numbers
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of a specific type.
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Backport PEP 3141 from the py3k branch to the trunk. This includes r50877 (just
the complex_pow part), r56649, r56652, r56715, r57296, r57302, r57359, r57361,
r57372, r57738, r57739, r58017, r58039, r58040, and r59390, and new
documentation. The only significant difference is that round(x) returns a float
to preserve backward-compatibility. See http://bugs.python.org/issue1689.
2008-01-02 22:21:52 -04:00
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All builtin numeric types support the following operations. See
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:ref:`power` and later sections for the operators' priorities.
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2007-08-15 11:28:01 -03:00
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+--------------------+---------------------------------+--------+
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| Operation | Result | Notes |
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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* | \(1) |
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+--------------------+---------------------------------+--------+
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Backport PEP 3141 from the py3k branch to the trunk. This includes r50877 (just
the complex_pow part), r56649, r56652, r56715, r57296, r57302, r57359, r57361,
r57372, r57738, r57739, r58017, r58039, r58040, and r59390, and new
documentation. The only significant difference is that round(x) returns a float
to preserve backward-compatibility. See http://bugs.python.org/issue1689.
2008-01-02 22:21:52 -04:00
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| ``x // y`` | (floored) quotient of *x* and | (4)(5) |
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2007-08-15 11:28:01 -03:00
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| | *y* | |
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+--------------------+---------------------------------+--------+
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| ``x % y`` | remainder of ``x / y`` | \(4) |
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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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+--------------------+---------------------------------+--------+
|
Backport PEP 3141 from the py3k branch to the trunk. This includes r50877 (just
the complex_pow part), r56649, r56652, r56715, r57296, r57302, r57359, r57361,
r57372, r57738, r57739, r58017, r58039, r58040, and r59390, and new
documentation. The only significant difference is that round(x) returns a float
to preserve backward-compatibility. See http://bugs.python.org/issue1689.
2008-01-02 22:21:52 -04:00
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| ``abs(x)`` | absolute value or magnitude of | \(3) |
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2007-08-15 11:28:01 -03:00
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| | *x* | |
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+--------------------+---------------------------------+--------+
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| ``int(x)`` | *x* converted to integer | \(2) |
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+--------------------+---------------------------------+--------+
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| ``long(x)`` | *x* converted to long integer | \(2) |
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+--------------------+---------------------------------+--------+
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2007-12-18 19:22:54 -04:00
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| ``float(x)`` | *x* converted to floating point | \(6) |
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2007-08-15 11:28:01 -03:00
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+--------------------+---------------------------------+--------+
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| ``complex(re,im)`` | a complex number with real part | |
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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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Backport PEP 3141 from the py3k branch to the trunk. This includes r50877 (just
the complex_pow part), r56649, r56652, r56715, r57296, r57302, r57359, r57361,
r57372, r57738, r57739, r58017, r58039, r58040, and r59390, and new
documentation. The only significant difference is that round(x) returns a float
to preserve backward-compatibility. See http://bugs.python.org/issue1689.
2008-01-02 22:21:52 -04:00
|
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| | *c*. (Identity on real numbers) | |
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2007-08-15 11:28:01 -03:00
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+--------------------+---------------------------------+--------+
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| ``divmod(x, y)`` | the pair ``(x // y, x % y)`` | (3)(4) |
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+--------------------+---------------------------------+--------+
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2008-01-06 11:41:50 -04:00
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| ``pow(x, y)`` | *x* to the power *y* | (3)(7) |
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2007-08-15 11:28:01 -03:00
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+--------------------+---------------------------------+--------+
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2008-01-06 11:41:50 -04:00
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| ``x ** y`` | *x* to the power *y* | \(7) |
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2007-08-15 11:28:01 -03:00
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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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.. index::
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pair: integer; division
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triple: long; integer; division
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For (plain or long) integer division, the result is an integer. The result is
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always rounded towards minus infinity: 1/2 is 0, (-1)/2 is -1, 1/(-2) is -1, and
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(-1)/(-2) is 0. Note that the result is a long integer if either operand is a
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long integer, regardless of the numeric value.
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(2)
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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)
|
2009-01-04 06:24:09 -04:00
|
|
|
single: trunc() (in module math)
|
2007-08-15 11:28:01 -03:00
|
|
|
pair: numeric; conversions
|
|
|
|
|
2009-01-03 18:05:22 -04:00
|
|
|
Conversion from floats using :func:`int` or :func:`long` truncates toward
|
|
|
|
zero like the related function, :func:`math.trunc`. Use the function
|
|
|
|
:func:`math.floor` to round downward and :func:`math.ceil` to round
|
|
|
|
upward.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
(3)
|
|
|
|
See :ref:`built-in-funcs` for a full description.
|
|
|
|
|
|
|
|
(4)
|
|
|
|
Complex floor division operator, modulo operator, and :func:`divmod`.
|
|
|
|
|
|
|
|
.. deprecated:: 2.3
|
|
|
|
Instead convert to float using :func:`abs` if appropriate.
|
|
|
|
|
|
|
|
(5)
|
|
|
|
Also referred to as integer division. The resultant value is a whole integer,
|
|
|
|
though the result's type is not necessarily int.
|
|
|
|
|
2007-12-18 19:22:54 -04:00
|
|
|
(6)
|
2009-01-03 16:55:06 -04:00
|
|
|
float also accepts the strings "nan" and "inf" with an optional prefix "+"
|
2007-12-18 19:22:54 -04:00
|
|
|
or "-" for Not a Number (NaN) and positive or negative infinity.
|
2009-01-03 16:55:06 -04:00
|
|
|
|
2007-12-18 19:22:54 -04:00
|
|
|
.. versionadded:: 2.6
|
|
|
|
|
2008-01-06 11:41:50 -04:00
|
|
|
(7)
|
|
|
|
Python defines ``pow(0, 0)`` and ``0 ** 0`` to be ``1``, as is common for
|
|
|
|
programming languages.
|
|
|
|
|
Backport PEP 3141 from the py3k branch to the trunk. This includes r50877 (just
the complex_pow part), r56649, r56652, r56715, r57296, r57302, r57359, r57361,
r57372, r57738, r57739, r58017, r58039, r58040, and r59390, and new
documentation. The only significant difference is that round(x) returns a float
to preserve backward-compatibility. See http://bugs.python.org/issue1689.
2008-01-02 22:21:52 -04:00
|
|
|
All :class:`numbers.Real` types (:class:`int`, :class:`long`, and
|
|
|
|
:class:`float`) also include the following operations:
|
|
|
|
|
2008-01-05 04:47:13 -04:00
|
|
|
+--------------------+------------------------------------+--------+
|
|
|
|
| Operation | Result | Notes |
|
|
|
|
+====================+====================================+========+
|
2009-01-18 06:48:16 -04:00
|
|
|
| ``math.trunc(x)`` | *x* truncated to Integral | |
|
2008-01-05 04:47:13 -04:00
|
|
|
+--------------------+------------------------------------+--------+
|
|
|
|
| ``round(x[, n])`` | *x* rounded to n digits, | |
|
|
|
|
| | rounding half to even. If n is | |
|
|
|
|
| | omitted, it defaults to 0. | |
|
|
|
|
+--------------------+------------------------------------+--------+
|
|
|
|
| ``math.floor(x)`` | the greatest integral float <= *x* | |
|
|
|
|
+--------------------+------------------------------------+--------+
|
|
|
|
| ``math.ceil(x)`` | the least integral float >= *x* | |
|
|
|
|
+--------------------+------------------------------------+--------+
|
2007-12-29 06:57:00 -04:00
|
|
|
|
|
|
|
.. XXXJH exceptions: overflow (when? what operations?) zerodivision
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
|
|
|
.. _bitstring-ops:
|
|
|
|
|
|
|
|
Bit-string Operations on Integer Types
|
|
|
|
--------------------------------------
|
|
|
|
|
|
|
|
.. _bit-string-operations:
|
|
|
|
|
|
|
|
Plain and long integer types support additional operations that make sense only
|
|
|
|
for bit-strings. Negative numbers are treated as their 2's complement value
|
|
|
|
(for long integers, this assumes a sufficiently large number of bits that no
|
|
|
|
overflow occurs during the operation).
|
|
|
|
|
2008-01-05 15:44:22 -04:00
|
|
|
The priorities of the binary bitwise operations are all lower than the numeric
|
2007-08-15 11:28:01 -03:00
|
|
|
operations and higher than the comparisons; the unary operation ``~`` has the
|
|
|
|
same priority as the other unary numeric operations (``+`` and ``-``).
|
|
|
|
|
2008-05-11 07:55:59 -03:00
|
|
|
This table lists the bit-string operations sorted in ascending priority:
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
+------------+--------------------------------+----------+
|
|
|
|
| Operation | Result | Notes |
|
|
|
|
+============+================================+==========+
|
|
|
|
| ``x | y`` | bitwise :dfn:`or` of *x* and | |
|
|
|
|
| | *y* | |
|
|
|
|
+------------+--------------------------------+----------+
|
|
|
|
| ``x ^ y`` | bitwise :dfn:`exclusive or` of | |
|
|
|
|
| | *x* and *y* | |
|
|
|
|
+------------+--------------------------------+----------+
|
|
|
|
| ``x & y`` | bitwise :dfn:`and` of *x* and | |
|
|
|
|
| | *y* | |
|
|
|
|
+------------+--------------------------------+----------+
|
2008-01-07 05:16:08 -04:00
|
|
|
| ``x << n`` | *x* shifted left by *n* bits | (1)(2) |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------+--------------------------------+----------+
|
2008-01-07 05:16:08 -04:00
|
|
|
| ``x >> n`` | *x* shifted right by *n* bits | (1)(3) |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------+--------------------------------+----------+
|
|
|
|
| ``~x`` | the bits of *x* inverted | |
|
|
|
|
+------------+--------------------------------+----------+
|
|
|
|
|
|
|
|
.. index::
|
|
|
|
triple: operations on; integer; types
|
|
|
|
pair: bit-string; operations
|
|
|
|
pair: shifting; operations
|
|
|
|
pair: masking; operations
|
|
|
|
|
|
|
|
Notes:
|
|
|
|
|
|
|
|
(1)
|
|
|
|
Negative shift counts are illegal and cause a :exc:`ValueError` to be raised.
|
|
|
|
|
|
|
|
(2)
|
2008-05-11 07:55:59 -03:00
|
|
|
A left shift by *n* bits is equivalent to multiplication by ``pow(2, n)``. A
|
|
|
|
long integer is returned if the result exceeds the range of plain integers.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
(3)
|
2008-05-11 07:55:59 -03:00
|
|
|
A right shift by *n* bits is equivalent to division by ``pow(2, n)``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
2008-12-17 12:14:37 -04:00
|
|
|
Additional Methods on Integer Types
|
|
|
|
-----------------------------------
|
|
|
|
|
|
|
|
.. method:: int.bit_length()
|
|
|
|
.. method:: long.bit_length()
|
|
|
|
|
2008-12-19 05:06:07 -04:00
|
|
|
Return the number of bits necessary to represent an integer in binary,
|
|
|
|
excluding the sign and leading zeros::
|
2008-12-17 12:14:37 -04:00
|
|
|
|
2008-12-19 05:06:07 -04:00
|
|
|
>>> n = -37
|
2008-12-17 12:14:37 -04:00
|
|
|
>>> bin(n)
|
2008-12-19 05:06:07 -04:00
|
|
|
'-0b100101'
|
2008-12-17 12:14:37 -04:00
|
|
|
>>> n.bit_length()
|
|
|
|
6
|
|
|
|
|
2008-12-19 05:06:07 -04:00
|
|
|
More precisely, if ``x`` is nonzero, then ``x.bit_length()`` is the
|
|
|
|
unique positive integer ``k`` such that ``2**(k-1) <= abs(x) < 2**k``.
|
|
|
|
Equivalently, when ``abs(x)`` is small enough to have a correctly
|
|
|
|
rounded logarithm, then ``k = 1 + int(log(abs(x), 2))``.
|
|
|
|
If ``x`` is zero, then ``x.bit_length()`` returns ``0``.
|
2008-12-17 12:14:37 -04:00
|
|
|
|
|
|
|
Equivalent to::
|
|
|
|
|
|
|
|
def bit_length(self):
|
2008-12-19 13:46:51 -04:00
|
|
|
s = bin(self) # binary representation: bin(-37) --> '-0b100101'
|
2008-12-19 05:06:07 -04:00
|
|
|
s = s.lstrip('-0b') # remove leading zeros and minus sign
|
|
|
|
return len(s) # len('100101') --> 6
|
2008-12-17 12:14:37 -04:00
|
|
|
|
|
|
|
.. versionadded:: 2.7
|
|
|
|
|
|
|
|
|
2008-07-15 16:08:33 -03:00
|
|
|
Additional Methods on Float
|
|
|
|
---------------------------
|
|
|
|
|
2008-09-12 23:11:51 -03:00
|
|
|
The float type has some 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.
|
2009-01-03 16:55:06 -04:00
|
|
|
|
2008-09-12 23:11:51 -03:00
|
|
|
.. versionadded:: 2.6
|
|
|
|
|
|
|
|
Two methods support conversion to
|
2008-07-15 16:08:33 -03:00
|
|
|
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.
|
|
|
|
|
|
|
|
.. versionadded:: 2.6
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: float.fromhex(s)
|
|
|
|
|
|
|
|
Class method to return the float represented by a hexadecimal
|
|
|
|
string *s*. The string *s* may have leading and trailing
|
|
|
|
whitespace.
|
|
|
|
|
|
|
|
.. versionadded:: 2.6
|
|
|
|
|
|
|
|
|
|
|
|
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'
|
|
|
|
|
|
|
|
|
2008-07-15 20:59:15 -03:00
|
|
|
.. _typeiter:
|
|
|
|
|
2007-08-15 11:28:01 -03:00
|
|
|
Iterator Types
|
|
|
|
==============
|
|
|
|
|
|
|
|
.. versionadded:: 2.2
|
|
|
|
|
|
|
|
.. 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:
|
|
|
|
|
2008-01-07 14:57:03 -04:00
|
|
|
.. XXX duplicated in reference/datamodel!
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-01-07 14:57:03 -04:00
|
|
|
.. method:: container.__iter__()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
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
|
|
|
|
:attr:`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 :attr:`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
|
|
|
|
:attr:`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.
|
|
|
|
|
|
|
|
The intention of the protocol is that once an iterator's :meth:`next` method
|
|
|
|
raises :exc:`StopIteration`, it will continue to do so on subsequent calls.
|
|
|
|
Implementations that do not obey this property are deemed broken. (This
|
|
|
|
constraint was added in Python 2.3; in Python 2.2, various iterators are broken
|
|
|
|
according to this rule.)
|
|
|
|
|
2007-10-21 07:52:38 -03:00
|
|
|
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:`next` methods.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
|
|
|
.. _typesseq:
|
|
|
|
|
|
|
|
Sequence Types --- :class:`str`, :class:`unicode`, :class:`list`, :class:`tuple`, :class:`buffer`, :class:`xrange`
|
|
|
|
==================================================================================================================
|
|
|
|
|
|
|
|
There are six sequence types: strings, Unicode strings, lists, tuples, buffers,
|
|
|
|
and xrange objects.
|
2009-01-18 06:45:22 -04:00
|
|
|
|
|
|
|
For other containers see the built in :class:`dict` and :class:`set` classes,
|
|
|
|
and the :mod:`collections` module.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
|
|
|
.. index::
|
|
|
|
object: sequence
|
|
|
|
object: string
|
|
|
|
object: Unicode
|
|
|
|
object: tuple
|
|
|
|
object: list
|
|
|
|
object: buffer
|
|
|
|
object: xrange
|
|
|
|
|
|
|
|
String literals are written in single or double quotes: ``'xyzzy'``,
|
|
|
|
``"frobozz"``. See :ref:`strings` for more about string literals.
|
|
|
|
Unicode strings are much like strings, but are specified in the syntax
|
|
|
|
using a preceding ``'u'`` character: ``u'abc'``, ``u"def"``. In addition
|
|
|
|
to the functionality described here, there are also string-specific
|
|
|
|
methods described in the :ref:`string-methods` section. Lists are
|
|
|
|
constructed with square brackets, separating items with commas: ``[a, b, c]``.
|
|
|
|
Tuples are constructed by the comma operator (not within square
|
|
|
|
brackets), with or without enclosing parentheses, but an empty tuple
|
|
|
|
must have the enclosing parentheses, such as ``a, b, c`` or ``()``. A
|
|
|
|
single item tuple must have a trailing comma, such as ``(d,)``.
|
|
|
|
|
|
|
|
Buffer objects are not directly supported by Python syntax, but can be created
|
|
|
|
by calling the builtin function :func:`buffer`. They don't support
|
|
|
|
concatenation or repetition.
|
|
|
|
|
|
|
|
Objects of type xrange are similar to buffers in that there is no specific syntax to
|
|
|
|
create them, but they are created using the :func:`xrange` function. They don't
|
|
|
|
support slicing, concatenation or repetition, and using ``in``, ``not in``,
|
|
|
|
:func:`min` or :func:`max` on them is inefficient.
|
|
|
|
|
|
|
|
Most sequence types support the following operations. The ``in`` and ``not in``
|
|
|
|
operations have the same priorities as the comparison operations. The ``+`` and
|
|
|
|
``*`` operations have the same priority as the corresponding numeric operations.
|
2008-01-07 12:42:08 -04:00
|
|
|
[#]_ Additional methods are provided for :ref:`typesseq-mutable`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
This table lists the sequence operations sorted in ascending priority
|
|
|
|
(operations in the same box have the same priority). In the table, *s* and *t*
|
|
|
|
are sequences of the same type; *n*, *i* and *j* are integers:
|
|
|
|
|
|
|
|
+------------------+--------------------------------+----------+
|
|
|
|
| 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) |
|
|
|
|
| | *t* | |
|
|
|
|
+------------------+--------------------------------+----------+
|
|
|
|
| ``s * n, n * s`` | *n* shallow copies of *s* | \(2) |
|
|
|
|
| | concatenated | |
|
|
|
|
+------------------+--------------------------------+----------+
|
|
|
|
| ``s[i]`` | *i*'th item of *s*, origin 0 | \(3) |
|
|
|
|
+------------------+--------------------------------+----------+
|
2008-01-07 05:16:08 -04:00
|
|
|
| ``s[i:j]`` | slice of *s* from *i* to *j* | (3)(4) |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------------+--------------------------------+----------+
|
2008-01-07 05:16:08 -04:00
|
|
|
| ``s[i:j:k]`` | slice of *s* from *i* to *j* | (3)(5) |
|
2007-08-15 11:28:01 -03:00
|
|
|
| | with step *k* | |
|
|
|
|
+------------------+--------------------------------+----------+
|
|
|
|
| ``len(s)`` | length of *s* | |
|
|
|
|
+------------------+--------------------------------+----------+
|
|
|
|
| ``min(s)`` | smallest item of *s* | |
|
|
|
|
+------------------+--------------------------------+----------+
|
|
|
|
| ``max(s)`` | largest item of *s* | |
|
|
|
|
+------------------+--------------------------------+----------+
|
|
|
|
|
|
|
|
Sequence types 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.)
|
|
|
|
|
|
|
|
.. index::
|
|
|
|
triple: operations on; sequence; types
|
|
|
|
builtin: len
|
|
|
|
builtin: min
|
|
|
|
builtin: max
|
|
|
|
pair: concatenation; operation
|
|
|
|
pair: repetition; operation
|
|
|
|
pair: subscript; operation
|
|
|
|
pair: slice; operation
|
|
|
|
pair: extended slice; operation
|
|
|
|
operator: in
|
|
|
|
operator: not in
|
|
|
|
|
|
|
|
Notes:
|
|
|
|
|
|
|
|
(1)
|
|
|
|
When *s* is a string or Unicode string object the ``in`` and ``not in``
|
|
|
|
operations act like a substring test. In Python versions before 2.3, *x* had to
|
|
|
|
be a string of length 1. In Python 2.3 and beyond, *x* may be a string of any
|
|
|
|
length.
|
|
|
|
|
|
|
|
(2)
|
|
|
|
Values of *n* less than ``0`` are treated as ``0`` (which yields an empty
|
|
|
|
sequence of the same type as *s*). Note also that the copies are shallow;
|
|
|
|
nested structures are not copied. This often haunts new Python programmers;
|
2008-03-22 19:04:10 -03:00
|
|
|
consider:
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
>>> 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 (pointers to) this single empty
|
|
|
|
list. Modifying any of the elements of ``lists`` modifies this single list.
|
2008-03-22 19:04:10 -03:00
|
|
|
You can create a list of different lists this way:
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
>>> lists = [[] for i in range(3)]
|
|
|
|
>>> lists[0].append(3)
|
|
|
|
>>> lists[1].append(5)
|
|
|
|
>>> lists[2].append(7)
|
|
|
|
>>> lists
|
|
|
|
[[3], [5], [7]]
|
|
|
|
|
|
|
|
(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
|
2007-12-16 11:53:49 -04:00
|
|
|
items with index ``x = i + n*k`` such that ``0 <= n < (j-i)/k``. In other words,
|
2007-08-15 11:28:01 -03:00
|
|
|
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)
|
|
|
|
If *s* and *t* are both strings, some Python implementations such as CPython can
|
|
|
|
usually perform an in-place optimization for assignments of the form ``s=s+t``
|
|
|
|
or ``s+=t``. When applicable, this optimization makes quadratic run-time much
|
|
|
|
less likely. This optimization is both version and implementation dependent.
|
|
|
|
For performance sensitive code, it is preferable to use the :meth:`str.join`
|
|
|
|
method which assures consistent linear concatenation performance across versions
|
|
|
|
and implementations.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.4
|
|
|
|
Formerly, string concatenation never occurred in-place.
|
|
|
|
|
|
|
|
|
|
|
|
.. _string-methods:
|
|
|
|
|
|
|
|
String Methods
|
|
|
|
--------------
|
|
|
|
|
|
|
|
.. index:: pair: string; methods
|
|
|
|
|
|
|
|
Below are listed the string methods which both 8-bit strings and Unicode objects
|
2007-09-20 13:45:27 -03:00
|
|
|
support. Note that none of these methods take keyword arguments.
|
|
|
|
|
|
|
|
In addition, Python's strings support the sequence type methods
|
2007-08-15 11:28:01 -03:00
|
|
|
described in the :ref:`typesseq` section. To output formatted strings
|
|
|
|
use template strings or the ``%`` operator described in the
|
|
|
|
:ref:`string-formatting` section. Also, see the :mod:`re` module for
|
|
|
|
string functions based on regular expressions.
|
|
|
|
|
|
|
|
.. method:: str.capitalize()
|
|
|
|
|
|
|
|
Return a copy of the string with only its first character capitalized.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.center(width[, fillchar])
|
|
|
|
|
|
|
|
Return centered in a string of length *width*. Padding is done using the
|
|
|
|
specified *fillchar* (default is a space).
|
|
|
|
|
|
|
|
.. versionchanged:: 2.4
|
|
|
|
Support for the *fillchar* argument.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.count(sub[, start[, end]])
|
|
|
|
|
2007-10-08 04:50:24 -03:00
|
|
|
Return the number of occurrences of substring *sub* in the range [*start*,
|
|
|
|
*end*]. Optional arguments *start* and *end* are interpreted as in slice
|
|
|
|
notation.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.decode([encoding[, errors]])
|
|
|
|
|
|
|
|
Decodes the string using the codec registered for *encoding*. *encoding*
|
|
|
|
defaults to the default string encoding. *errors* may be given to set a
|
|
|
|
different error handling scheme. The default is ``'strict'``, meaning that
|
|
|
|
encoding errors raise :exc:`UnicodeError`. Other possible values are
|
|
|
|
``'ignore'``, ``'replace'`` and any other name registered via
|
|
|
|
:func:`codecs.register_error`, see section :ref:`codec-base-classes`.
|
|
|
|
|
|
|
|
.. versionadded:: 2.2
|
|
|
|
|
|
|
|
.. versionchanged:: 2.3
|
|
|
|
Support for other error handling schemes added.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.encode([encoding[,errors]])
|
|
|
|
|
|
|
|
Return an encoded version of the string. Default encoding is the current
|
|
|
|
default string encoding. *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:`codec-base-classes`. For a list of possible encodings, see section
|
|
|
|
:ref:`standard-encodings`.
|
|
|
|
|
|
|
|
.. versionadded:: 2.0
|
|
|
|
|
|
|
|
.. versionchanged:: 2.3
|
|
|
|
Support for ``'xmlcharrefreplace'`` and ``'backslashreplace'`` and other error
|
|
|
|
handling schemes 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.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.5
|
|
|
|
Accept tuples as *suffix*.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.expandtabs([tabsize])
|
|
|
|
|
2007-10-08 04:50:24 -03:00
|
|
|
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. The
|
|
|
|
column number is reset to zero after each newline occurring in the string.
|
|
|
|
If *tabsize* is not given, a tab size of ``8`` characters is assumed. This
|
|
|
|
doesn't understand other non-printing characters or escape sequences.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
|
|
|
.. 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 range [*start*, *end*]. Optional arguments *start*
|
|
|
|
and *end* are interpreted as in slice notation. Return ``-1`` if *sub* is not
|
|
|
|
found.
|
|
|
|
|
|
|
|
|
2008-05-12 13:45:43 -03:00
|
|
|
.. method:: str.format(format_string, *args, **kwargs)
|
|
|
|
|
|
|
|
Perform a string formatting operation. The *format_string* argument 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 *format_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.
|
|
|
|
|
|
|
|
This method of string formatting is the new standard in Python 3.0, and
|
|
|
|
should be preferred to the ``%`` formatting described in
|
|
|
|
:ref:`string-formatting` in new code.
|
|
|
|
|
|
|
|
.. versionadded:: 2.6
|
|
|
|
|
|
|
|
|
2007-08-15 11:28:01 -03:00
|
|
|
.. method:: str.index(sub[, start[, end]])
|
|
|
|
|
|
|
|
Like :meth:`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.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.isalpha()
|
|
|
|
|
|
|
|
Return true if all characters in the string are alphabetic and there is at least
|
|
|
|
one character, false otherwise.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.isdigit()
|
|
|
|
|
|
|
|
Return true if all characters in the string are digits and there is at least one
|
|
|
|
character, false otherwise.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.islower()
|
|
|
|
|
|
|
|
Return true if all cased characters in the string are lowercase and there is at
|
|
|
|
least one cased character, false otherwise.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.isspace()
|
|
|
|
|
|
|
|
Return true if there are only whitespace characters in the string and there is
|
|
|
|
at least one character, false otherwise.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. 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.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.isupper()
|
|
|
|
|
|
|
|
Return true if all cased characters in the string are uppercase and there is at
|
|
|
|
least one cased character, false otherwise.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.join(seq)
|
|
|
|
|
|
|
|
Return a string which is the concatenation of the strings in the sequence *seq*.
|
|
|
|
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 a space). The original string is
|
|
|
|
returned if *width* is less than ``len(s)``.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.4
|
|
|
|
Support for the *fillchar* argument.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.lower()
|
|
|
|
|
|
|
|
Return a copy of the string converted to lowercase.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. 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*
|
2008-03-22 19:04:10 -03:00
|
|
|
argument is not a prefix; rather, all combinations of its values are stripped:
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
>>> ' spacious '.lstrip()
|
|
|
|
'spacious '
|
|
|
|
>>> 'www.example.com'.lstrip('cmowz.')
|
|
|
|
'example.com'
|
|
|
|
|
|
|
|
.. versionchanged:: 2.2.2
|
|
|
|
Support for the *chars* argument.
|
|
|
|
|
|
|
|
|
|
|
|
.. 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.
|
|
|
|
|
|
|
|
.. versionadded:: 2.5
|
|
|
|
|
|
|
|
|
|
|
|
.. 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 a space). The original string is
|
|
|
|
returned if *width* is less than ``len(s)``.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.4
|
|
|
|
Support for the *fillchar* argument.
|
|
|
|
|
|
|
|
|
|
|
|
.. 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.
|
|
|
|
|
|
|
|
.. versionadded:: 2.5
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.rsplit([sep [,maxsplit]])
|
|
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
|
.. versionadded:: 2.4
|
|
|
|
|
|
|
|
|
|
|
|
.. 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*
|
2008-03-22 19:04:10 -03:00
|
|
|
argument is not a suffix; rather, all combinations of its values are stripped:
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
>>> ' spacious '.rstrip()
|
|
|
|
' spacious'
|
|
|
|
>>> 'mississippi'.rstrip('ipz')
|
|
|
|
'mississ'
|
|
|
|
|
|
|
|
.. versionchanged:: 2.2.2
|
|
|
|
Support for the *chars* argument.
|
|
|
|
|
|
|
|
|
2007-10-08 04:50:24 -03:00
|
|
|
.. method:: str.split([sep[, maxsplit]])
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2007-10-08 04:50:24 -03:00
|
|
|
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, then there is no limit on the number of splits (all possible
|
|
|
|
splits are made).
|
|
|
|
|
2007-11-01 17:37:02 -03:00
|
|
|
If *sep* is given, consecutive delimiters are not grouped together and are
|
2007-10-08 04:50:24 -03:00
|
|
|
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 ``['']``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
If *sep* is not specified or is ``None``, a different splitting algorithm is
|
2007-10-08 04:50:24 -03:00
|
|
|
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()`` returns ``['1', '2', '3']``, and
|
|
|
|
``' 1 2 3 '.split(None, 1)`` returns ``['1', '2 3 ']``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
|
|
|
.. 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.
|
|
|
|
|
|
|
|
|
|
|
|
.. 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.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.5
|
|
|
|
Accept tuples as *prefix*.
|
|
|
|
|
|
|
|
|
|
|
|
.. 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
|
2008-03-22 19:04:10 -03:00
|
|
|
values are stripped:
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
>>> ' spacious '.strip()
|
|
|
|
'spacious'
|
|
|
|
>>> 'www.example.com'.strip('cmowz.')
|
|
|
|
'example'
|
|
|
|
|
|
|
|
.. versionchanged:: 2.2.2
|
|
|
|
Support for the *chars* argument.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.swapcase()
|
|
|
|
|
|
|
|
Return a copy of the string with uppercase characters converted to lowercase and
|
|
|
|
vice versa.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.title()
|
|
|
|
|
|
|
|
Return a titlecased version of the string: words start with uppercase
|
|
|
|
characters, all remaining cased characters are lowercase.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.translate(table[, deletechars])
|
|
|
|
|
|
|
|
Return a copy of the string where all characters occurring in the optional
|
|
|
|
argument *deletechars* are removed, and the remaining characters have been
|
|
|
|
mapped through the given translation table, which must be a string of length
|
|
|
|
256.
|
|
|
|
|
|
|
|
You can use the :func:`maketrans` helper function in the :mod:`string` module to
|
|
|
|
create a translation table. For string objects, set the *table* argument to
|
2008-03-22 19:04:10 -03:00
|
|
|
``None`` for translations that only delete characters:
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
>>> 'read this short text'.translate(None, 'aeiou')
|
|
|
|
'rd ths shrt txt'
|
|
|
|
|
|
|
|
.. versionadded:: 2.6
|
|
|
|
Support for a ``None`` *table* argument.
|
|
|
|
|
|
|
|
For Unicode objects, the :meth:`translate` method does not accept the optional
|
|
|
|
*deletechars* argument. Instead, it returns a copy of the *s* where all
|
|
|
|
characters have been mapped through the given translation table which must be a
|
|
|
|
mapping of Unicode ordinals to Unicode ordinals, Unicode strings or ``None``.
|
|
|
|
Unmapped characters are left untouched. Characters mapped to ``None`` are
|
|
|
|
deleted. Note, a more flexible approach is to create a custom character mapping
|
|
|
|
codec using the :mod:`codecs` module (see :mod:`encodings.cp1251` for an
|
|
|
|
example).
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.upper()
|
|
|
|
|
|
|
|
Return a copy of the string converted to uppercase.
|
|
|
|
|
|
|
|
For 8-bit strings, this method is locale-dependent.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: str.zfill(width)
|
|
|
|
|
2007-10-08 04:50:24 -03:00
|
|
|
Return the numeric string left filled with zeros in a string of length
|
|
|
|
*width*. A sign prefix is handled correctly. The original string is
|
|
|
|
returned if *width* is less than ``len(s)``.
|
2009-01-03 16:55:06 -04:00
|
|
|
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
.. versionadded:: 2.2.2
|
|
|
|
|
2008-03-17 16:33:11 -03:00
|
|
|
The following methods are present only on unicode objects:
|
|
|
|
|
|
|
|
.. method:: unicode.isnumeric()
|
|
|
|
|
|
|
|
Return ``True`` if there are only numeric characters in S, ``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.
|
2009-01-03 16:55:06 -04:00
|
|
|
|
2008-03-17 16:33:11 -03:00
|
|
|
.. method:: unicode.isdecimal()
|
|
|
|
|
|
|
|
Return ``True`` if there are only decimal characters in S, ``False``
|
|
|
|
otherwise. Decimal characters include digit characters, and all characters
|
|
|
|
that that can be used to form decimal-radix numbers, e.g. U+0660,
|
|
|
|
ARABIC-INDIC DIGIT ZERO.
|
|
|
|
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
.. _string-formatting:
|
|
|
|
|
|
|
|
String Formatting Operations
|
|
|
|
----------------------------
|
|
|
|
|
|
|
|
.. 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
|
|
|
|
|
|
|
|
String and Unicode 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
|
|
|
|
or Unicode object), ``%`` conversion specifications in *format* are replaced
|
|
|
|
with zero or more elements of *values*. The effect is similar to the using
|
|
|
|
:cfunc:`sprintf` in the C language. If *format* is a Unicode object, or if any
|
|
|
|
of the objects being converted using the ``%s`` conversion are Unicode objects,
|
|
|
|
the result will also be a Unicode object.
|
|
|
|
|
|
|
|
If *format* requires a single argument, *values* may be a single non-tuple
|
|
|
|
object. [#]_ 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 width 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
|
2008-03-22 19:04:10 -03:00
|
|
|
selects the value to be formatted from the mapping. For example:
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
>>> print '%(language)s has %(#)03d quote types.' % \
|
2008-03-22 19:04:10 -03:00
|
|
|
... {'language': "Python", "#": 2}
|
2007-08-15 11:28:01 -03:00
|
|
|
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
|
2008-05-11 06:06:30 -03:00
|
|
|
is not necessary for Python -- so e.g. ``%ld`` is identical to ``%d``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
The conversion types are:
|
|
|
|
|
|
|
|
+------------+-----------------------------------------------------+-------+
|
|
|
|
| Conversion | Meaning | Notes |
|
|
|
|
+============+=====================================================+=======+
|
|
|
|
| ``'d'`` | Signed integer decimal. | |
|
|
|
|
+------------+-----------------------------------------------------+-------+
|
|
|
|
| ``'i'`` | Signed integer decimal. | |
|
|
|
|
+------------+-----------------------------------------------------+-------+
|
2008-05-11 06:06:30 -03:00
|
|
|
| ``'o'`` | Signed octal value. | \(1) |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------+-----------------------------------------------------+-------+
|
2008-05-11 06:06:30 -03:00
|
|
|
| ``'u'`` | Obselete type -- it is identical to ``'d'``. | \(7) |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------+-----------------------------------------------------+-------+
|
2008-05-11 06:06:30 -03:00
|
|
|
| ``'x'`` | Signed hexadecimal (lowercase). | \(2) |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------+-----------------------------------------------------+-------+
|
2008-05-11 06:06:30 -03:00
|
|
|
| ``'X'`` | Signed hexadecimal (uppercase). | \(2) |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------+-----------------------------------------------------+-------+
|
|
|
|
| ``'e'`` | Floating point exponential format (lowercase). | \(3) |
|
|
|
|
+------------+-----------------------------------------------------+-------+
|
|
|
|
| ``'E'`` | Floating point exponential format (uppercase). | \(3) |
|
|
|
|
+------------+-----------------------------------------------------+-------+
|
2008-07-17 16:49:47 -03:00
|
|
|
| ``'f'`` | Floating point decimal format. | \(3) |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------+-----------------------------------------------------+-------+
|
2008-07-17 16:49:47 -03:00
|
|
|
| ``'F'`` | Floating point decimal format. | \(3) |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------+-----------------------------------------------------+-------+
|
2008-05-06 14:11:42 -03:00
|
|
|
| ``'g'`` | Floating point format. Uses lowercase exponential | \(4) |
|
2008-05-06 14:20:54 -03:00
|
|
|
| | format if exponent is less than -4 or not less than | |
|
2008-05-06 14:11:42 -03:00
|
|
|
| | precision, decimal format otherwise. | |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------+-----------------------------------------------------+-------+
|
2008-05-06 14:11:42 -03:00
|
|
|
| ``'G'`` | Floating point format. Uses uppercase exponential | \(4) |
|
2008-05-06 14:20:54 -03:00
|
|
|
| | format if exponent is less than -4 or not less than | |
|
2008-05-06 14:11:42 -03:00
|
|
|
| | precision, decimal format otherwise. | |
|
2007-08-15 11:28:01 -03:00
|
|
|
+------------+-----------------------------------------------------+-------+
|
|
|
|
| ``'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 | \(6) |
|
|
|
|
| | :func:`str`). | |
|
|
|
|
+------------+-----------------------------------------------------+-------+
|
|
|
|
| ``'%'`` | 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)
|
|
|
|
The ``%r`` conversion was added in Python 2.0.
|
|
|
|
|
|
|
|
The precision determines the maximal number of characters used.
|
|
|
|
|
|
|
|
(6)
|
|
|
|
If the object or format provided is a :class:`unicode` string, the resulting
|
|
|
|
string will also be :class:`unicode`.
|
|
|
|
|
|
|
|
The precision determines the maximal number of characters used.
|
|
|
|
|
2008-05-11 06:06:30 -03:00
|
|
|
(7)
|
|
|
|
See :pep:`237`.
|
|
|
|
|
2007-08-15 11:28:01 -03:00
|
|
|
Since Python strings have an explicit length, ``%s`` conversions do not assume
|
|
|
|
that ``'\0'`` is the end of the string.
|
|
|
|
|
2007-12-29 06:57:00 -04:00
|
|
|
.. XXX Examples?
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
For safety reasons, floating point precisions are clipped to 50; ``%f``
|
|
|
|
conversions for numbers whose absolute value is over 1e25 are replaced by ``%g``
|
|
|
|
conversions. [#]_ All other errors raise exceptions.
|
|
|
|
|
|
|
|
.. index::
|
|
|
|
module: string
|
|
|
|
module: re
|
|
|
|
|
|
|
|
Additional string operations are defined in standard modules :mod:`string` and
|
|
|
|
:mod:`re`.
|
|
|
|
|
|
|
|
|
|
|
|
.. _typesseq-xrange:
|
|
|
|
|
|
|
|
XRange Type
|
|
|
|
-----------
|
|
|
|
|
|
|
|
.. index:: object: xrange
|
|
|
|
|
|
|
|
The :class:`xrange` type is an immutable sequence which is commonly used for
|
|
|
|
looping. The advantage of the :class:`xrange` type is that an :class:`xrange`
|
|
|
|
object will always take the same amount of memory, no matter the size of the
|
|
|
|
range it represents. There are no consistent performance advantages.
|
|
|
|
|
|
|
|
XRange objects have very little behavior: they only support indexing, iteration,
|
|
|
|
and the :func:`len` function.
|
|
|
|
|
|
|
|
|
|
|
|
.. _typesseq-mutable:
|
|
|
|
|
|
|
|
Mutable Sequence Types
|
|
|
|
----------------------
|
|
|
|
|
|
|
|
.. index::
|
|
|
|
triple: mutable; sequence; types
|
|
|
|
object: list
|
|
|
|
|
|
|
|
List objects support additional operations that allow in-place modification of
|
|
|
|
the object. Other mutable sequence types (when added to the language) should
|
|
|
|
also support these operations. Strings and tuples are immutable sequence types:
|
|
|
|
such objects cannot be modified once created. The following operations are
|
|
|
|
defined on mutable sequence types (where *x* is an arbitrary object):
|
|
|
|
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
|
|
|
| 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)`` | same as ``s[len(s):len(s)] = | \(2) |
|
|
|
|
| | [x]`` | |
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
|
|
|
| ``s.extend(x)`` | same as ``s[len(s):len(s)] = | \(3) |
|
|
|
|
| | x`` | |
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
|
|
|
| ``s.count(x)`` | return number of *i*'s for | |
|
|
|
|
| | which ``s[i] == x`` | |
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
|
|
|
| ``s.index(x[, i[, j]])`` | return smallest *k* such that | \(4) |
|
|
|
|
| | ``s[k] == x`` and ``i <= k < | |
|
|
|
|
| | j`` | |
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
|
|
|
| ``s.insert(i, x)`` | same as ``s[i:i] = [x]`` | \(5) |
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
|
|
|
| ``s.pop([i])`` | same as ``x = s[i]; del s[i]; | \(6) |
|
|
|
|
| | return x`` | |
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
|
|
|
| ``s.remove(x)`` | same as ``del s[s.index(x)]`` | \(4) |
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
|
|
|
| ``s.reverse()`` | reverses the items of *s* in | \(7) |
|
|
|
|
| | place | |
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
2008-01-07 05:16:08 -04:00
|
|
|
| ``s.sort([cmp[, key[, | sort the items of *s* in place | (7)(8)(9)(10) |
|
2007-08-15 11:28:01 -03:00
|
|
|
| reverse]]])`` | | |
|
|
|
|
+------------------------------+--------------------------------+---------------------+
|
|
|
|
|
|
|
|
.. index::
|
|
|
|
triple: operations on; sequence; types
|
|
|
|
triple: operations on; list; type
|
|
|
|
pair: subscript; assignment
|
|
|
|
pair: slice; assignment
|
|
|
|
pair: extended slice; assignment
|
|
|
|
statement: del
|
|
|
|
single: append() (list method)
|
|
|
|
single: extend() (list method)
|
|
|
|
single: count() (list method)
|
|
|
|
single: index() (list method)
|
|
|
|
single: insert() (list method)
|
|
|
|
single: pop() (list method)
|
|
|
|
single: remove() (list method)
|
|
|
|
single: reverse() (list method)
|
|
|
|
single: sort() (list method)
|
|
|
|
|
|
|
|
Notes:
|
|
|
|
|
|
|
|
(1)
|
|
|
|
*t* must have the same length as the slice it is replacing.
|
|
|
|
|
|
|
|
(2)
|
|
|
|
The C implementation of Python has historically accepted multiple parameters and
|
|
|
|
implicitly joined them into a tuple; this no longer works in Python 2.0. Use of
|
|
|
|
this misfeature has been deprecated since Python 1.4.
|
|
|
|
|
|
|
|
(3)
|
|
|
|
*x* can be any iterable object.
|
|
|
|
|
|
|
|
(4)
|
|
|
|
Raises :exc:`ValueError` when *x* is not found in *s*. When a negative index is
|
|
|
|
passed as the second or third parameter to the :meth:`index` method, the list
|
|
|
|
length is added, as for slice indices. If it is still negative, it is truncated
|
|
|
|
to zero, as for slice indices.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.3
|
|
|
|
Previously, :meth:`index` didn't have arguments for specifying start and stop
|
|
|
|
positions.
|
|
|
|
|
|
|
|
(5)
|
|
|
|
When a negative index is passed as the first parameter to the :meth:`insert`
|
|
|
|
method, the list length is added, as for slice indices. If it is still
|
|
|
|
negative, it is truncated to zero, as for slice indices.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.3
|
|
|
|
Previously, all negative indices were truncated to zero.
|
|
|
|
|
|
|
|
(6)
|
|
|
|
The :meth:`pop` method is only supported by the list and array types. The
|
|
|
|
optional argument *i* defaults to ``-1``, so that by default the last item is
|
|
|
|
removed and returned.
|
|
|
|
|
|
|
|
(7)
|
|
|
|
The :meth:`sort` and :meth:`reverse` methods modify the list in place for
|
|
|
|
economy of space when sorting or reversing a large list. To remind you that
|
|
|
|
they operate by side effect, they don't return the sorted or reversed list.
|
|
|
|
|
|
|
|
(8)
|
|
|
|
The :meth:`sort` method takes optional arguments for controlling the
|
|
|
|
comparisons.
|
|
|
|
|
|
|
|
*cmp* specifies a custom comparison function of two arguments (list items) which
|
|
|
|
should return a negative, zero or positive number depending on whether the first
|
|
|
|
argument is considered smaller than, equal to, or larger than the second
|
2008-01-06 11:34:57 -04:00
|
|
|
argument: ``cmp=lambda x,y: cmp(x.lower(), y.lower())``. The default value
|
|
|
|
is ``None``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
*key* specifies a function of one argument that is used to extract a comparison
|
2008-01-06 11:34:57 -04:00
|
|
|
key from each list element: ``key=str.lower``. The default value is ``None``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
*reverse* is a boolean value. If set to ``True``, then the list elements are
|
|
|
|
sorted as if each comparison were reversed.
|
|
|
|
|
|
|
|
In general, the *key* and *reverse* conversion processes are much faster than
|
|
|
|
specifying an equivalent *cmp* function. This is because *cmp* is called
|
|
|
|
multiple times for each list element while *key* and *reverse* touch each
|
|
|
|
element only once.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.3
|
|
|
|
Support for ``None`` as an equivalent to omitting *cmp* was added.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.4
|
|
|
|
Support for *key* and *reverse* was added.
|
|
|
|
|
|
|
|
(9)
|
|
|
|
Starting with Python 2.3, 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).
|
|
|
|
|
|
|
|
(10)
|
|
|
|
While a list is being sorted, the effect of attempting to mutate, or even
|
|
|
|
inspect, the list is undefined. The C implementation of Python 2.3 and newer
|
|
|
|
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.
|
|
|
|
|
|
|
|
|
|
|
|
.. _types-set:
|
|
|
|
|
|
|
|
Set Types --- :class:`set`, :class:`frozenset`
|
|
|
|
==============================================
|
|
|
|
|
|
|
|
.. index:: object: set
|
|
|
|
|
2007-11-02 17:06:17 -03:00
|
|
|
A :dfn:`set` object is an unordered collection of distinct :term:`hashable` objects.
|
2007-08-15 11:28:01 -03:00
|
|
|
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.)
|
|
|
|
|
|
|
|
|
|
|
|
.. versionadded:: 2.4
|
|
|
|
|
|
|
|
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 builtin set types, :class:`set` and :class:`frozenset`.
|
|
|
|
The :class:`set` type is mutable --- the contents can be changed using methods
|
|
|
|
like :meth:`add` and :meth:`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.
|
2007-11-02 17:06:17 -03:00
|
|
|
The :class:`frozenset` type is immutable and :term:`hashable` --- its contents cannot be
|
2007-08-15 11:28:01 -03:00
|
|
|
altered after it is created; it can therefore be used as a dictionary key or as
|
|
|
|
an element of another set.
|
|
|
|
|
|
|
|
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 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.
|
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Instances of :class:`set` and :class:`frozenset` provide the following
|
|
|
|
operations:
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. describe:: len(s)
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return the cardinality of set *s*.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. describe:: x in s
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Test *x* for membership in *s*.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. describe:: x not in s
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Test *x* for non-membership in *s*.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: isdisjoint(other)
|
2007-11-07 22:52:43 -04:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return True if the set has no elements in common with *other*. Sets are
|
2008-07-12 17:16:19 -03:00
|
|
|
disjoint if and only if their intersection is the empty set.
|
2007-11-07 22:52:43 -04:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. versionadded:: 2.6
|
2007-11-07 22:52:43 -04:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: issubset(other)
|
|
|
|
set <= other
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Test whether every element in the set is in *other*.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: set < other
|
2007-09-01 12:49:49 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Test whether the set is a true subset of *other*, that is,
|
|
|
|
``set <= other and set != other``.
|
2007-09-01 12:49:49 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: issuperset(other)
|
|
|
|
set >= other
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Test whether every element in *other* is in the set.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: set > other
|
2007-09-01 12:49:49 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Test whether the set is a true superset of *other*, that is, ``set >=
|
|
|
|
other and set != other``.
|
2007-09-01 12:49:49 -03:00
|
|
|
|
2008-06-09 05:33:37 -03:00
|
|
|
.. method:: union(other, ...)
|
|
|
|
set | other | ...
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2009-01-18 06:42:35 -04:00
|
|
|
Return a new set with elements from the set and all others.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-06-09 05:33:37 -03:00
|
|
|
.. versionchanged:: 2.6
|
|
|
|
Accepts multiple input iterables.
|
|
|
|
|
2008-06-09 10:07:27 -03:00
|
|
|
.. method:: intersection(other, ...)
|
|
|
|
set & other & ...
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2009-01-18 06:42:35 -04:00
|
|
|
Return a new set with elements common to the set and all others.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-06-09 10:07:27 -03:00
|
|
|
.. versionchanged:: 2.6
|
|
|
|
Accepts multiple input iterables.
|
|
|
|
|
2008-06-11 07:30:54 -03:00
|
|
|
.. method:: difference(other, ...)
|
|
|
|
set - other - ...
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-06-11 07:30:54 -03:00
|
|
|
Return a new set with elements in the set that are not in the others.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.6
|
|
|
|
Accepts multiple input iterables.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: symmetric_difference(other)
|
|
|
|
set ^ other
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return a new set with elements in either the set or *other* but not both.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: copy()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return a new set with a shallow copy of *s*.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
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')``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
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).
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
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')])``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
The subset and equality comparisons do not generalize to a complete ordering
|
|
|
|
function. For example, any two 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``. Accordingly, sets do not implement the :meth:`__cmp__`
|
|
|
|
method.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Since sets only define partial ordering (subset relationships), the output of
|
|
|
|
the :meth:`list.sort` method is undefined for lists of sets.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Set elements, like dictionary keys, must be :term:`hashable`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
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`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
The following table lists operations available for :class:`set` that do not
|
|
|
|
apply to immutable instances of :class:`frozenset`:
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-06-09 05:33:37 -03:00
|
|
|
.. method:: update(other, ...)
|
|
|
|
set |= other | ...
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Update the set, adding elements from *other*.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-06-09 05:33:37 -03:00
|
|
|
.. versionchanged:: 2.6
|
|
|
|
Accepts multiple input iterables.
|
|
|
|
|
2008-06-09 10:07:27 -03:00
|
|
|
.. method:: intersection_update(other, ...)
|
|
|
|
set &= other & ...
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Update the set, keeping only elements found in it and *other*.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-06-09 10:07:27 -03:00
|
|
|
.. versionchanged:: 2.6
|
|
|
|
Accepts multiple input iterables.
|
|
|
|
|
2008-06-11 07:30:54 -03:00
|
|
|
.. method:: difference_update(other, ...)
|
|
|
|
set -= other | ...
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-06-11 07:30:54 -03:00
|
|
|
Update the set, removing elements found in others.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.6
|
|
|
|
Accepts multiple input iterables.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: symmetric_difference_update(other)
|
|
|
|
set ^= other
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Update the set, keeping only elements found in either set, but not in both.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: add(elem)
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Add element *elem* to the set.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: remove(elem)
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Remove element *elem* from the set. Raises :exc:`KeyError` if *elem* is
|
|
|
|
not contained in the set.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: discard(elem)
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Remove element *elem* from the set if it is present.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: pop()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Remove and return an arbitrary element from the set. Raises
|
|
|
|
:exc:`KeyError` if the set is empty.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: clear()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Remove all elements from the set.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
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.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
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.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
|
|
|
.. seealso::
|
|
|
|
|
2007-11-29 13:01:20 -04:00
|
|
|
:ref:`comparison-to-builtin-set`
|
2007-08-15 11:28:01 -03:00
|
|
|
Differences between the :mod:`sets` module and the built-in set types.
|
|
|
|
|
|
|
|
|
|
|
|
.. _typesmapping:
|
|
|
|
|
|
|
|
Mapping Types --- :class:`dict`
|
|
|
|
===============================
|
|
|
|
|
|
|
|
.. index::
|
|
|
|
object: mapping
|
|
|
|
object: dictionary
|
|
|
|
triple: operations on; mapping; types
|
|
|
|
triple: operations on; dictionary; type
|
|
|
|
statement: del
|
|
|
|
builtin: len
|
|
|
|
|
2007-11-02 17:06:17 -03:00
|
|
|
A :dfn:`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.)
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
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([arg])
|
|
|
|
|
|
|
|
Return a new dictionary initialized from an optional positional argument or from
|
|
|
|
a set of keyword arguments. If no arguments are given, return a new empty
|
|
|
|
dictionary. If the positional argument *arg* is a mapping object, return a
|
|
|
|
dictionary mapping the same keys to the same values as does the mapping object.
|
|
|
|
Otherwise the positional argument must be a sequence, a container that supports
|
|
|
|
iteration, or an iterator object. The elements of the argument must each also
|
|
|
|
be of one of those kinds, and each must in turn contain exactly two objects.
|
|
|
|
The first is used as a key in the new dictionary, and the second as the key's
|
|
|
|
value. If a given key is seen more than once, the last value associated with it
|
|
|
|
is retained in the new dictionary.
|
|
|
|
|
|
|
|
If keyword arguments are given, the keywords themselves with their associated
|
|
|
|
values are added as items to the dictionary. If a key is specified both in the
|
|
|
|
positional argument and as a keyword argument, the value associated with the
|
|
|
|
keyword is retained in the dictionary. For example, these all return a
|
|
|
|
dictionary equal to ``{"one": 2, "two": 3}``:
|
|
|
|
|
|
|
|
* ``dict(one=2, two=3)``
|
|
|
|
|
|
|
|
* ``dict({'one': 2, 'two': 3})``
|
|
|
|
|
|
|
|
* ``dict(zip(('one', 'two'), (2, 3)))``
|
|
|
|
|
|
|
|
* ``dict([['two', 3], ['one', 2]])``
|
|
|
|
|
|
|
|
The first example only works for keys that are valid Python
|
|
|
|
identifiers; the others work with any valid keys.
|
|
|
|
|
|
|
|
.. versionadded:: 2.2
|
|
|
|
|
|
|
|
.. versionchanged:: 2.3
|
|
|
|
Support for building a dictionary from keyword arguments added.
|
|
|
|
|
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
These are the operations that dictionaries support (and therefore, custom
|
|
|
|
mapping types should support too):
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. describe:: len(d)
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return the number of items in the dictionary *d*.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. describe:: d[key]
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return the item of *d* with key *key*. Raises a :exc:`KeyError` if *key*
|
|
|
|
is not in the map.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2009-01-03 16:55:06 -04:00
|
|
|
.. versionadded:: 2.5
|
2008-05-09 18:30:26 -03:00
|
|
|
If a subclass of dict defines a method :meth:`__missing__`, if the key
|
|
|
|
*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
|
|
|
|
if the key is not present. 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. For an example, see
|
|
|
|
:class:`collections.defaultdict`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. describe:: d[key] = value
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Set ``d[key]`` to *value*.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. describe:: del d[key]
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Remove ``d[key]`` from *d*. Raises a :exc:`KeyError` if *key* is not in the
|
|
|
|
map.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. describe:: key in d
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return ``True`` if *d* has a key *key*, else ``False``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. versionadded:: 2.2
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. describe:: key not in d
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Equivalent to ``not key in d``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. versionadded:: 2.2
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: clear()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Remove all items from the dictionary.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: copy()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return a shallow copy of the dictionary.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: fromkeys(seq[, value])
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Create a new dictionary with keys from *seq* and values set to *value*.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
:func:`fromkeys` is a class method that returns a new dictionary. *value*
|
|
|
|
defaults to ``None``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. versionadded:: 2.3
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: get(key[, default])
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
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`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: has_key(key)
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-10-31 17:41:44 -03:00
|
|
|
Test for the presence of *key* in the dictionary. :meth:`has_key` is
|
|
|
|
deprecated in favor of ``key in d``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: items()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return a copy of the dictionary's list of ``(key, value)`` pairs.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. note::
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Keys and values are listed in an arbitrary order which is non-random,
|
|
|
|
varies across Python implementations, and depends on the dictionary's
|
|
|
|
history of insertions and deletions. If :meth:`items`, :meth:`keys`,
|
|
|
|
:meth:`values`, :meth:`iteritems`, :meth:`iterkeys`, and
|
|
|
|
:meth:`itervalues` are called with no intervening modifications to the
|
|
|
|
dictionary, the lists will directly correspond. This allows the
|
|
|
|
creation of ``(value, key)`` pairs using :func:`zip`: ``pairs =
|
|
|
|
zip(d.values(), d.keys())``. The same relationship holds for the
|
|
|
|
:meth:`iterkeys` and :meth:`itervalues` methods: ``pairs =
|
|
|
|
zip(d.itervalues(), d.iterkeys())`` provides the same value for
|
|
|
|
``pairs``. Another way to create the same list is ``pairs = [(v, k) for
|
|
|
|
(k, v) in d.iteritems()]``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: iteritems()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return an iterator over the dictionary's ``(key, value)`` pairs. See the
|
|
|
|
note for :meth:`dict.items`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. versionadded:: 2.2
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: iterkeys()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return an iterator over the dictionary's keys. See the note for
|
|
|
|
:meth:`dict.items`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. versionadded:: 2.2
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: itervalues()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return an iterator over the dictionary's values. See the note for
|
|
|
|
:meth:`dict.items`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. versionadded:: 2.2
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: keys()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return a copy of the dictionary's list of keys. See the note for
|
|
|
|
:meth:`dict.items`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: pop(key[, default])
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
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.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. versionadded:: 2.3
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: popitem()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Remove and return an arbitrary ``(key, value)`` pair from the dictionary.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
:func:`popitem` is useful to destructively iterate over a dictionary, as
|
|
|
|
often used in set algorithms. If the dictionary is empty, calling
|
|
|
|
:func:`popitem` raises a :exc:`KeyError`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: setdefault(key[, default])
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
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``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: update([other])
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Update the dictionary with the key/value pairs from *other*, overwriting
|
|
|
|
existing keys. Return ``None``.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
:func:`update` accepts either another dictionary object or an iterable of
|
|
|
|
key/value pairs (as a tuple or other iterable of length two). If keyword
|
|
|
|
arguments are specified, the dictionary is then is updated with those
|
|
|
|
key/value pairs: ``d.update(red=1, blue=2)``.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.4
|
|
|
|
Allowed the argument to be an iterable of key/value pairs and allowed
|
|
|
|
keyword arguments.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
.. method:: values()
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-05-09 18:30:26 -03:00
|
|
|
Return a copy of the dictionary's list of values. See the note for
|
|
|
|
:meth:`dict.items`.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
|
|
|
.. _bltin-file-objects:
|
|
|
|
|
|
|
|
File Objects
|
|
|
|
============
|
|
|
|
|
|
|
|
.. index::
|
|
|
|
object: file
|
|
|
|
builtin: file
|
|
|
|
module: os
|
|
|
|
module: socket
|
|
|
|
|
|
|
|
File objects are implemented using C's ``stdio`` package and can be
|
2007-12-29 06:57:00 -04:00
|
|
|
created with the built-in :func:`open` function. File
|
2007-08-15 11:28:01 -03:00
|
|
|
objects are also returned by some other built-in functions and methods,
|
|
|
|
such as :func:`os.popen` and :func:`os.fdopen` and the :meth:`makefile`
|
2007-11-02 05:24:59 -03:00
|
|
|
method of socket objects. Temporary files can be created using the
|
|
|
|
:mod:`tempfile` module, and high-level file operations such as copying,
|
|
|
|
moving, and deleting files and directories can be achieved with the
|
|
|
|
:mod:`shutil` module.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
When a file operation fails for an I/O-related reason, the exception
|
|
|
|
:exc:`IOError` is raised. This includes situations where the operation is not
|
|
|
|
defined for some reason, like :meth:`seek` on a tty device or writing a file
|
|
|
|
opened for reading.
|
|
|
|
|
|
|
|
Files have the following methods:
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.close()
|
|
|
|
|
|
|
|
Close the file. A closed file cannot be read or written any more. Any operation
|
|
|
|
which requires that the file be open will raise a :exc:`ValueError` after the
|
|
|
|
file has been closed. Calling :meth:`close` more than once is allowed.
|
|
|
|
|
|
|
|
As of Python 2.5, you can avoid having to call this method explicitly if you use
|
|
|
|
the :keyword:`with` statement. For example, the following code will
|
2007-12-29 06:57:00 -04:00
|
|
|
automatically close *f* when the :keyword:`with` block is exited::
|
2007-08-15 11:28:01 -03:00
|
|
|
|
2008-07-29 16:28:49 -03:00
|
|
|
from __future__ import with_statement # This isn't required in Python 2.6
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
with open("hello.txt") as f:
|
|
|
|
for line in f:
|
|
|
|
print line
|
|
|
|
|
|
|
|
In older versions of Python, you would have needed to do this to get the same
|
|
|
|
effect::
|
|
|
|
|
|
|
|
f = open("hello.txt")
|
|
|
|
try:
|
|
|
|
for line in f:
|
|
|
|
print line
|
|
|
|
finally:
|
|
|
|
f.close()
|
|
|
|
|
|
|
|
.. note::
|
|
|
|
|
|
|
|
Not all "file-like" types in Python support use as a context manager for the
|
|
|
|
:keyword:`with` statement. If your code is intended to work with any file-like
|
|
|
|
object, you can use the function :func:`contextlib.closing` instead of using
|
|
|
|
the object directly.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.flush()
|
|
|
|
|
|
|
|
Flush the internal buffer, like ``stdio``'s :cfunc:`fflush`. This may be a
|
|
|
|
no-op on some file-like objects.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.fileno()
|
|
|
|
|
|
|
|
.. index::
|
2007-10-21 07:45:46 -03:00
|
|
|
pair: file; descriptor
|
2007-08-15 11:28:01 -03:00
|
|
|
module: fcntl
|
|
|
|
|
|
|
|
Return the integer "file descriptor" that is used by the underlying
|
|
|
|
implementation to request I/O operations from the operating system. This can be
|
|
|
|
useful for other, lower level interfaces that use file descriptors, such as the
|
|
|
|
:mod:`fcntl` module or :func:`os.read` and friends.
|
|
|
|
|
|
|
|
.. note::
|
|
|
|
|
|
|
|
File-like objects which do not have a real file descriptor should *not* provide
|
|
|
|
this method!
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.isatty()
|
|
|
|
|
|
|
|
Return ``True`` if the file is connected to a tty(-like) device, else ``False``.
|
|
|
|
|
|
|
|
.. note::
|
|
|
|
|
|
|
|
If a file-like object is not associated with a real file, this method should
|
|
|
|
*not* be implemented.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.next()
|
|
|
|
|
|
|
|
A file object is its own iterator, for example ``iter(f)`` returns *f* (unless
|
|
|
|
*f* is closed). When a file is used as an iterator, typically in a
|
|
|
|
:keyword:`for` loop (for example, ``for line in f: print line``), the
|
|
|
|
:meth:`next` method is called repeatedly. This method returns the next input
|
|
|
|
line, or raises :exc:`StopIteration` when EOF is hit when the file is open for
|
|
|
|
reading (behavior is undefined when the file is open for writing). In order to
|
|
|
|
make a :keyword:`for` loop the most efficient way of looping over the lines of a
|
|
|
|
file (a very common operation), the :meth:`next` method uses a hidden read-ahead
|
|
|
|
buffer. As a consequence of using a read-ahead buffer, combining :meth:`next`
|
|
|
|
with other file methods (like :meth:`readline`) does not work right. However,
|
|
|
|
using :meth:`seek` to reposition the file to an absolute position will flush the
|
|
|
|
read-ahead buffer.
|
|
|
|
|
|
|
|
.. versionadded:: 2.3
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.read([size])
|
|
|
|
|
|
|
|
Read at most *size* bytes from the file (less if the read hits EOF before
|
|
|
|
obtaining *size* bytes). If the *size* argument is negative or omitted, read
|
|
|
|
all data until EOF is reached. The bytes are returned as a string object. An
|
|
|
|
empty string is returned when EOF is encountered immediately. (For certain
|
|
|
|
files, like ttys, it makes sense to continue reading after an EOF is hit.) Note
|
|
|
|
that this method may call the underlying C function :cfunc:`fread` more than
|
|
|
|
once in an effort to acquire as close to *size* bytes as possible. Also note
|
2008-07-03 09:50:03 -03:00
|
|
|
that when in non-blocking mode, less data than was requested may be
|
2007-08-15 11:28:01 -03:00
|
|
|
returned, even if no *size* parameter was given.
|
|
|
|
|
2008-07-01 17:45:09 -03:00
|
|
|
.. note::
|
2008-07-26 10:08:19 -03:00
|
|
|
This function is simply a wrapper for the underlying
|
|
|
|
:cfunc:`fread` C function, and will behave the same in corner cases,
|
|
|
|
such as whether the EOF value is cached.
|
2008-07-01 17:45:09 -03:00
|
|
|
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
.. method:: file.readline([size])
|
|
|
|
|
|
|
|
Read one entire line from the file. A trailing newline character is kept in the
|
|
|
|
string (but may be absent when a file ends with an incomplete line). [#]_ If
|
|
|
|
the *size* argument is present and non-negative, it is a maximum byte count
|
|
|
|
(including the trailing newline) and an incomplete line may be returned. An
|
|
|
|
empty string is returned *only* when EOF is encountered immediately.
|
|
|
|
|
|
|
|
.. note::
|
|
|
|
|
|
|
|
Unlike ``stdio``'s :cfunc:`fgets`, the returned string contains null characters
|
|
|
|
(``'\0'``) if they occurred in the input.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.readlines([sizehint])
|
|
|
|
|
|
|
|
Read until EOF using :meth:`readline` and return a list containing the lines
|
|
|
|
thus read. If the optional *sizehint* argument is present, instead of
|
|
|
|
reading up to EOF, whole lines totalling approximately *sizehint* bytes
|
|
|
|
(possibly after rounding up to an internal buffer size) are read. Objects
|
|
|
|
implementing a file-like interface may choose to ignore *sizehint* if it
|
|
|
|
cannot be implemented, or cannot be implemented efficiently.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.xreadlines()
|
|
|
|
|
|
|
|
This method returns the same thing as ``iter(f)``.
|
|
|
|
|
|
|
|
.. versionadded:: 2.1
|
|
|
|
|
|
|
|
.. deprecated:: 2.3
|
|
|
|
Use ``for line in file`` instead.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.seek(offset[, whence])
|
|
|
|
|
|
|
|
Set the file's current position, like ``stdio``'s :cfunc:`fseek`. The *whence*
|
|
|
|
argument is optional and defaults to ``os.SEEK_SET`` or ``0`` (absolute file
|
|
|
|
positioning); other values are ``os.SEEK_CUR`` or ``1`` (seek relative to the
|
|
|
|
current position) and ``os.SEEK_END`` or ``2`` (seek relative to the file's
|
2008-01-05 15:44:22 -04:00
|
|
|
end). There is no return value.
|
2009-01-03 16:55:06 -04:00
|
|
|
|
2008-01-05 15:44:22 -04:00
|
|
|
For example, ``f.seek(2, os.SEEK_CUR)`` advances the position by two and
|
|
|
|
``f.seek(-3, os.SEEK_END)`` sets the position to the third to last.
|
|
|
|
|
|
|
|
Note that if the file is opened for appending
|
2007-08-15 11:28:01 -03:00
|
|
|
(mode ``'a'`` or ``'a+'``), any :meth:`seek` operations will be undone at the
|
|
|
|
next write. If the file is only opened for writing in append mode (mode
|
|
|
|
``'a'``), this method is essentially a no-op, but it remains useful for files
|
|
|
|
opened in append mode with reading enabled (mode ``'a+'``). If the file is
|
|
|
|
opened in text mode (without ``'b'``), only offsets returned by :meth:`tell` are
|
|
|
|
legal. Use of other offsets causes undefined behavior.
|
|
|
|
|
|
|
|
Note that not all file objects are seekable.
|
|
|
|
|
|
|
|
.. versionchanged:: 2.6
|
2007-12-29 06:57:00 -04:00
|
|
|
Passing float values as offset has been deprecated.
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.tell()
|
|
|
|
|
|
|
|
Return the file's current position, like ``stdio``'s :cfunc:`ftell`.
|
|
|
|
|
|
|
|
.. note::
|
|
|
|
|
|
|
|
On Windows, :meth:`tell` can return illegal values (after an :cfunc:`fgets`)
|
|
|
|
when reading files with Unix-style line-endings. Use binary mode (``'rb'``) to
|
|
|
|
circumvent this problem.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.truncate([size])
|
|
|
|
|
|
|
|
Truncate the file's size. If the optional *size* argument is present, the file
|
|
|
|
is truncated to (at most) that size. The size defaults to the current position.
|
|
|
|
The current file position is not changed. Note that if a specified size exceeds
|
|
|
|
the file's current size, the result is platform-dependent: possibilities
|
|
|
|
include that the file may remain unchanged, increase to the specified size as if
|
|
|
|
zero-filled, or increase to the specified size with undefined new content.
|
|
|
|
Availability: Windows, many Unix variants.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.write(str)
|
|
|
|
|
|
|
|
Write a string to the file. There is no return value. Due to buffering, the
|
|
|
|
string may not actually show up in the file until the :meth:`flush` or
|
|
|
|
:meth:`close` method is called.
|
|
|
|
|
|
|
|
|
|
|
|
.. method:: file.writelines(sequence)
|
|
|
|
|
|
|
|
Write a sequence of strings to the file. The sequence can be any iterable
|
|
|
|
object producing strings, typically a list of strings. There is no return value.
|
|
|
|
(The name is intended to match :meth:`readlines`; :meth:`writelines` does not
|
|
|
|
add line separators.)
|
|
|
|
|
|
|
|
Files support the iterator protocol. Each iteration returns the same result as
|
|
|
|
``file.readline()``, and iteration ends when the :meth:`readline` method returns
|
|
|
|
an empty string.
|
|
|
|
|
|
|
|
File objects also offer a number of other interesting attributes. These are not
|
|
|
|
required for file-like objects, but should be implemented if they make sense for
|
|
|
|
the particular object.
|
|
|
|
|
|
|
|
|
|
|
|
.. attribute:: file.closed
|
|
|
|
|
|
|
|
bool indicating the current state of the file object. This is a read-only
|
|
|
|
attribute; the :meth:`close` method changes the value. It may not be available
|
|
|
|
on all file-like objects.
|
|
|
|
|
|
|
|
|
|
|
|
.. attribute:: file.encoding
|
|
|
|
|
|
|
|
The encoding that this file uses. When Unicode strings are written to a file,
|
|
|
|
they will be converted to byte strings using this encoding. In addition, when
|
|
|
|
the file is connected to a terminal, the attribute gives the encoding that the
|
|
|
|
terminal is likely to use (that information might be incorrect if the user has
|
|
|
|
misconfigured the terminal). The attribute is read-only and may not be present
|
|
|
|
on all file-like objects. It may also be ``None``, in which case the file uses
|
|
|
|
the system default encoding for converting Unicode strings.
|
|
|
|
|
|
|
|
.. versionadded:: 2.3
|
|
|
|
|
|
|
|
|
2008-06-01 04:20:46 -03:00
|
|
|
.. attribute:: file.errors
|
|
|
|
|
2008-06-20 20:14:32 -03:00
|
|
|
The Unicode error handler used along with the encoding.
|
2008-06-01 04:20:46 -03:00
|
|
|
|
|
|
|
.. versionadded:: 2.6
|
|
|
|
|
|
|
|
|
2007-08-15 11:28:01 -03:00
|
|
|
.. attribute:: file.mode
|
|
|
|
|
|
|
|
The I/O mode for the file. If the file was created using the :func:`open`
|
|
|
|
built-in function, this will be the value of the *mode* parameter. This is a
|
|
|
|
read-only attribute and may not be present on all file-like objects.
|
|
|
|
|
|
|
|
|
|
|
|
.. attribute:: file.name
|
|
|
|
|
|
|
|
If the file object was created using :func:`open`, the name of the file.
|
|
|
|
Otherwise, some string that indicates the source of the file object, of the
|
|
|
|
form ``<...>``. This is a read-only attribute and may not be present on all
|
|
|
|
file-like objects.
|
|
|
|
|
|
|
|
|
|
|
|
.. attribute:: file.newlines
|
|
|
|
|
|
|
|
If Python was built with the :option:`--with-universal-newlines` option to
|
|
|
|
:program:`configure` (the default) this read-only attribute exists, and for
|
|
|
|
files opened in universal newline read mode it keeps track of the types of
|
|
|
|
newlines encountered while reading the file. The values it can take are
|
|
|
|
``'\r'``, ``'\n'``, ``'\r\n'``, ``None`` (unknown, no newlines read yet) or a
|
|
|
|
tuple containing all the newline types seen, to indicate that multiple newline
|
|
|
|
conventions were encountered. For files not opened in universal newline read
|
|
|
|
mode the value of this attribute will be ``None``.
|
|
|
|
|
|
|
|
|
|
|
|
.. attribute:: file.softspace
|
|
|
|
|
|
|
|
Boolean that indicates whether a space character needs to be printed before
|
|
|
|
another value when using the :keyword:`print` statement. Classes that are trying
|
|
|
|
to simulate a file object should also have a writable :attr:`softspace`
|
|
|
|
attribute, which should be initialized to zero. This will be automatic for most
|
|
|
|
classes implemented in Python (care may be needed for objects that override
|
|
|
|
attribute access); types implemented in C will have to provide a writable
|
|
|
|
:attr:`softspace` attribute.
|
|
|
|
|
|
|
|
.. note::
|
|
|
|
|
|
|
|
This attribute is not used to control the :keyword:`print` statement, but to
|
|
|
|
allow the implementation of :keyword:`print` to keep track of its internal
|
|
|
|
state.
|
|
|
|
|
|
|
|
|
|
|
|
.. _typecontextmanager:
|
|
|
|
|
|
|
|
Context Manager Types
|
|
|
|
=====================
|
|
|
|
|
|
|
|
.. versionadded:: 2.5
|
|
|
|
|
|
|
|
.. 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 two separate 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.
|
|
|
|
|
|
|
|
The :dfn:`context management protocol` consists of a pair of methods that need
|
|
|
|
to be provided for a context manager object to define a runtime context:
|
|
|
|
|
|
|
|
|
|
|
|
.. 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 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
|
2008-01-06 11:30:34 -04:00
|
|
|
returned by :func:`decimal.localcontext`. These managers set the active
|
2007-08-15 11:28:01 -03:00
|
|
|
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)
|
|
|
|
|
2007-10-18 00:44:48 -03:00
|
|
|
Exit the runtime context and return a Boolean flag indicating if any exception
|
2007-08-15 11:28:01 -03:00
|
|
|
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 (such as ``contextlib.nested``) 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.
|
|
|
|
|
2007-12-02 10:58:50 -04:00
|
|
|
Python's :term:`generator`\s and the ``contextlib.contextfactory`` :term:`decorator`
|
|
|
|
provide a convenient way to implement these protocols. If a generator function is
|
2007-08-15 11:28:01 -03:00
|
|
|
decorated with the ``contextlib.contextfactory`` 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 member of every module is :attr:`__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.
|
|
|
|
|
|
|
|
The implementation adds two special read-only attributes to class instance
|
|
|
|
methods: ``m.im_self`` is the object on which the method operates, and
|
|
|
|
``m.im_func`` is the function implementing the method. Calling ``m(arg-1,
|
|
|
|
arg-2, ..., arg-n)`` is completely equivalent to calling ``m.im_func(m.im_self,
|
|
|
|
arg-1, arg-2, ..., arg-n)``.
|
|
|
|
|
|
|
|
Class instance methods are either *bound* or *unbound*, referring to whether the
|
|
|
|
method was accessed through an instance or a class, respectively. When a method
|
|
|
|
is unbound, its ``im_self`` attribute will be ``None`` and if called, an
|
|
|
|
explicit ``self`` object must be passed as the first argument. In this case,
|
|
|
|
``self`` must be an instance of the unbound method's class (or a subclass of
|
|
|
|
that class), otherwise a :exc:`TypeError` is raised.
|
|
|
|
|
|
|
|
Like function objects, methods objects support getting arbitrary attributes.
|
|
|
|
However, since method attributes are actually stored on the underlying function
|
|
|
|
object (``meth.im_func``), setting method attributes on either bound or unbound
|
|
|
|
methods is disallowed. Attempting to set a method attribute results in a
|
|
|
|
:exc:`TypeError` 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.im_func.whoami = 'my name is c'
|
|
|
|
|
|
|
|
See :ref:`types` for more information.
|
|
|
|
|
|
|
|
|
|
|
|
.. _bltin-code-objects:
|
|
|
|
|
|
|
|
Code Objects
|
|
|
|
------------
|
|
|
|
|
|
|
|
.. index:: object: code
|
|
|
|
|
|
|
|
.. index::
|
|
|
|
builtin: compile
|
|
|
|
single: func_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:`func_code`
|
|
|
|
attribute. See also the :mod:`code` module.
|
|
|
|
|
|
|
|
.. index::
|
|
|
|
statement: exec
|
|
|
|
builtin: eval
|
|
|
|
|
|
|
|
A code object can be executed or evaluated by passing it (instead of a source
|
|
|
|
string) to the :keyword:`exec` statement or the built-in :func:`eval` function.
|
|
|
|
|
|
|
|
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: ``<type '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).
|
|
|
|
|
|
|
|
It is written as ``None``.
|
|
|
|
|
|
|
|
|
|
|
|
.. _bltin-ellipsis-object:
|
|
|
|
|
|
|
|
The Ellipsis Object
|
|
|
|
-------------------
|
|
|
|
|
|
|
|
This object is used by extended slice notation (see :ref:`slicings`). It
|
|
|
|
supports no special operations. There is exactly one ellipsis object, named
|
|
|
|
:const:`Ellipsis` (a built-in name).
|
|
|
|
|
|
|
|
It is written as ``Ellipsis``.
|
|
|
|
|
|
|
|
|
|
|
|
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 cast any value to a Boolean,
|
|
|
|
if the value can be interpreted as a truth value (see section Truth Value
|
|
|
|
Testing 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:: object.__methods__
|
|
|
|
|
|
|
|
.. deprecated:: 2.2
|
|
|
|
Use the built-in function :func:`dir` to get a list of an object's attributes.
|
|
|
|
This attribute is no longer available.
|
|
|
|
|
|
|
|
|
|
|
|
.. attribute:: object.__members__
|
|
|
|
|
|
|
|
.. deprecated:: 2.2
|
|
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Use the built-in function :func:`dir` to get a list of an object's attributes.
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This attribute is no longer available.
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.. attribute:: instance.__class__
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The class to which a class instance belongs.
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.. attribute:: class.__bases__
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The tuple of base classes of a class object. If there are no base classes, this
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will be an empty tuple.
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.. attribute:: class.__name__
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The name of the class or type.
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.. rubric:: Footnotes
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.. [#] Additional information on these special methods may be found in the Python
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Reference Manual (:ref:`customization`).
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.. [#] 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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.. [#] They must have since the parser can't tell the type of the operands.
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.. [#] 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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.. [#] These numbers are fairly arbitrary. They are intended to avoid printing endless
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strings of meaningless digits without hampering correct use and without having
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to know the exact precision of floating point values on a particular machine.
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.. [#] The advantage of leaving the newline on is that returning an empty string is
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then an unambiguous EOF indication. It is also possible (in cases where it
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might matter, for example, if you want to make an exact copy of a file while
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scanning its lines) to tell whether the last line of a file ended in a newline
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or not (yes this happens!).
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