1548 lines
65 KiB
ReStructuredText
1548 lines
65 KiB
ReStructuredText
.. XXX document all delegations to __special__ methods
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.. _built-in-funcs:
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Built-in Functions
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==================
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The Python interpreter has a number of functions and types built into it that
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are always available. They are listed here in alphabetical order.
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=================== ================= ================== ================ ====================
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.. .. Built-in Functions .. ..
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=================== ================= ================== ================ ====================
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:func:`abs` |func-dict|_ :func:`help` :func:`min` :func:`setattr`
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:func:`all` :func:`dir` :func:`hex` :func:`next` :func:`slice`
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:func:`any` :func:`divmod` :func:`id` :func:`object` :func:`sorted`
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:func:`ascii` :func:`enumerate` :func:`input` :func:`oct` :func:`staticmethod`
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:func:`bin` :func:`eval` :func:`int` :func:`open` |func-str|_
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:func:`bool` :func:`exec` :func:`isinstance` :func:`ord` :func:`sum`
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:func:`bytearray` :func:`filter` :func:`issubclass` :func:`pow` :func:`super`
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:func:`bytes` :func:`float` :func:`iter` :func:`print` |func-tuple|_
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:func:`callable` :func:`format` :func:`len` :func:`property` :func:`type`
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:func:`chr` |func-frozenset|_ |func-list|_ |func-range|_ :func:`vars`
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:func:`classmethod` :func:`getattr` :func:`locals` :func:`repr` :func:`zip`
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:func:`compile` :func:`globals` :func:`map` :func:`reversed` :func:`__import__`
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:func:`complex` :func:`hasattr` :func:`max` :func:`round`
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:func:`delattr` :func:`hash` |func-memoryview|_ |func-set|_
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=================== ================= ================== ================ ====================
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.. using :func:`dict` would create a link to another page, so local targets are
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used, with replacement texts to make the output in the table consistent
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.. |func-dict| replace:: ``dict()``
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.. |func-frozenset| replace:: ``frozenset()``
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.. |func-memoryview| replace:: ``memoryview()``
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.. |func-set| replace:: ``set()``
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.. |func-list| replace:: ``list()``
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.. |func-str| replace:: ``str()``
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.. |func-tuple| replace:: ``tuple()``
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.. |func-range| replace:: ``range()``
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.. function:: abs(x)
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Return the absolute value of a number. The argument may be an
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integer or a floating point number. If the argument is a complex number, its
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magnitude is returned.
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.. function:: all(iterable)
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Return ``True`` if all elements of the *iterable* are true (or if the iterable
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is empty). Equivalent to::
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def all(iterable):
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for element in iterable:
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if not element:
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return False
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return True
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.. function:: any(iterable)
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Return ``True`` if any element of the *iterable* is true. If the iterable
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is empty, return ``False``. Equivalent to::
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def any(iterable):
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for element in iterable:
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if element:
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return True
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return False
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.. function:: ascii(object)
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As :func:`repr`, return a string containing a printable representation of an
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object, but escape the non-ASCII characters in the string returned by
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:func:`repr` using ``\x``, ``\u`` or ``\U`` escapes. This generates a string
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similar to that returned by :func:`repr` in Python 2.
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.. function:: bin(x)
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Convert an integer number to a binary string. The result is a valid Python
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expression. If *x* is not a Python :class:`int` object, it has to define an
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:meth:`__index__` method that returns an integer.
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.. function:: bool([x])
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Convert a value to a Boolean, using the standard :ref:`truth testing
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procedure <truth>`. If *x* is false or omitted, this returns ``False``;
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otherwise it returns ``True``. :class:`bool` is also a class, which is a
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subclass of :class:`int` (see :ref:`typesnumeric`). Class :class:`bool`
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cannot be subclassed further. Its only instances are ``False`` and
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``True`` (see :ref:`bltin-boolean-values`).
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.. index:: pair: Boolean; type
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.. _func-bytearray:
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.. function:: bytearray([source[, encoding[, errors]]])
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Return a new array of bytes. The :class:`bytearray` type is a mutable
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sequence of integers in the range 0 <= x < 256. It has most of the usual
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methods of mutable sequences, described in :ref:`typesseq-mutable`, as well
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as most methods that the :class:`bytes` type has, see :ref:`bytes-methods`.
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The optional *source* parameter can be used to initialize the array in a few
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different ways:
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* If it is a *string*, you must also give the *encoding* (and optionally,
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*errors*) parameters; :func:`bytearray` then converts the string to
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bytes using :meth:`str.encode`.
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* If it is an *integer*, the array will have that size and will be
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initialized with null bytes.
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* If it is an object conforming to the *buffer* interface, a read-only buffer
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of the object will be used to initialize the bytes array.
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* If it is an *iterable*, it must be an iterable of integers in the range
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``0 <= x < 256``, which are used as the initial contents of the array.
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Without an argument, an array of size 0 is created.
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See also :ref:`binaryseq` and :ref:`typebytearray`.
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.. _func-bytes:
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.. function:: bytes([source[, encoding[, errors]]])
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Return a new "bytes" object, which is an immutable sequence of integers in
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the range ``0 <= x < 256``. :class:`bytes` is an immutable version of
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:class:`bytearray` -- it has the same non-mutating methods and the same
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indexing and slicing behavior.
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Accordingly, constructor arguments are interpreted as for :func:`bytearray`.
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Bytes objects can also be created with literals, see :ref:`strings`.
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See also :ref:`binaryseq`, :ref:`typebytes`, and :ref:`bytes-methods`.
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.. function:: callable(object)
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Return :const:`True` if the *object* argument appears callable,
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:const:`False` if not. If this returns true, it is still possible that a
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call fails, but if it is false, calling *object* will never succeed.
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Note that classes are callable (calling a class returns a new instance);
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instances are callable if their class has a :meth:`__call__` method.
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.. versionadded:: 3.2
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This function was first removed in Python 3.0 and then brought back
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in Python 3.2.
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.. function:: chr(i)
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Return the string representing a character whose Unicode codepoint is the integer
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*i*. For example, ``chr(97)`` returns the string ``'a'``. This is the
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inverse of :func:`ord`. The valid range for the argument is from 0 through
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1,114,111 (0x10FFFF in base 16). :exc:`ValueError` will be raised if *i* is
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outside that range.
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.. function:: classmethod(function)
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Return a class method for *function*.
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A class method receives the class as implicit first argument, just like an
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instance method receives the instance. To declare a class method, use this
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idiom::
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class C:
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@classmethod
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def f(cls, arg1, arg2, ...): ...
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The ``@classmethod`` form is a function :term:`decorator` -- see the description
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of function definitions in :ref:`function` for details.
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It can be called either on the class (such as ``C.f()``) or on an instance (such
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as ``C().f()``). The instance is ignored except for its class. If a class
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method is called for a derived class, the derived class object is passed as the
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implied first argument.
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Class methods are different than C++ or Java static methods. If you want those,
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see :func:`staticmethod` in this section.
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For more information on class methods, consult the documentation on the standard
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type hierarchy in :ref:`types`.
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.. function:: compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1)
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Compile the *source* into a code or AST object. Code objects can be executed
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by :func:`exec` or :func:`eval`. *source* can either be a normal string, a
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byte string, or an AST object. Refer to the :mod:`ast` module documentation
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for information on how to work with AST objects.
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The *filename* argument should give the file from which the code was read;
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pass some recognizable value if it wasn't read from a file (``'<string>'`` is
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commonly used).
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The *mode* argument specifies what kind of code must be compiled; it can be
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``'exec'`` if *source* consists of a sequence of statements, ``'eval'`` if it
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consists of a single expression, or ``'single'`` if it consists of a single
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interactive statement (in the latter case, expression statements that
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evaluate to something other than ``None`` will be printed).
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The optional arguments *flags* and *dont_inherit* control which future
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statements (see :pep:`236`) affect the compilation of *source*. If neither
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is present (or both are zero) the code is compiled with those future
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statements that are in effect in the code that is calling compile. If the
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*flags* argument is given and *dont_inherit* is not (or is zero) then the
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future statements specified by the *flags* argument are used in addition to
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those that would be used anyway. If *dont_inherit* is a non-zero integer then
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the *flags* argument is it -- the future statements in effect around the call
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to compile are ignored.
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Future statements are specified by bits which can be bitwise ORed together to
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specify multiple statements. The bitfield required to specify a given feature
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can be found as the :attr:`~__future__._Feature.compiler_flag` attribute on
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the :class:`~__future__._Feature` instance in the :mod:`__future__` module.
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The argument *optimize* specifies the optimization level of the compiler; the
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default value of ``-1`` selects the optimization level of the interpreter as
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given by :option:`-O` options. Explicit levels are ``0`` (no optimization;
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``__debug__`` is true), ``1`` (asserts are removed, ``__debug__`` is false)
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or ``2`` (docstrings are removed too).
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This function raises :exc:`SyntaxError` if the compiled source is invalid,
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and :exc:`TypeError` if the source contains null bytes.
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.. note::
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When compiling a string with multi-line code in ``'single'`` or
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``'eval'`` mode, input must be terminated by at least one newline
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character. This is to facilitate detection of incomplete and complete
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statements in the :mod:`code` module.
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.. versionchanged:: 3.2
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Allowed use of Windows and Mac newlines. Also input in ``'exec'`` mode
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does not have to end in a newline anymore. Added the *optimize* parameter.
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.. function:: complex([real[, imag]])
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Create a complex number with the value *real* + *imag*\*j or convert a string or
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number to a complex number. If the first parameter is a string, it will be
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interpreted as a complex number and the function must be called without a second
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parameter. The second parameter can never be a string. Each argument may be any
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numeric type (including complex). If *imag* is omitted, it defaults to zero and
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the function serves as a numeric conversion function like :func:`int`
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and :func:`float`. If both arguments are omitted, returns ``0j``.
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.. note::
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When converting from a string, the string must not contain whitespace
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around the central ``+`` or ``-`` operator. For example,
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``complex('1+2j')`` is fine, but ``complex('1 + 2j')`` raises
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:exc:`ValueError`.
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The complex type is described in :ref:`typesnumeric`.
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.. function:: delattr(object, name)
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This is a relative of :func:`setattr`. The arguments are an object and a
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string. The string must be the name of one of the object's attributes. The
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function deletes the named attribute, provided the object allows it. For
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example, ``delattr(x, 'foobar')`` is equivalent to ``del x.foobar``.
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.. _func-dict:
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.. function:: dict(**kwarg)
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dict(mapping, **kwarg)
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dict(iterable, **kwarg)
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:noindex:
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Create a new dictionary. The :class:`dict` object is the dictionary class.
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See :class:`dict` and :ref:`typesmapping` for documentation about this
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class.
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For other containers see the built-in :class:`list`, :class:`set`, and
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:class:`tuple` classes, as well as the :mod:`collections` module.
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.. function:: dir([object])
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Without arguments, return the list of names in the current local scope. With an
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argument, attempt to return a list of valid attributes for that object.
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If the object has a method named :meth:`__dir__`, this method will be called and
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must return the list of attributes. This allows objects that implement a custom
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:func:`__getattr__` or :func:`__getattribute__` function to customize the way
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:func:`dir` reports their attributes.
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If the object does not provide :meth:`__dir__`, the function tries its best to
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gather information from the object's :attr:`__dict__` attribute, if defined, and
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from its type object. The resulting list is not necessarily complete, and may
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be inaccurate when the object has a custom :func:`__getattr__`.
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The default :func:`dir` mechanism behaves differently with different types of
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objects, as it attempts to produce the most relevant, rather than complete,
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information:
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* If the object is a module object, the list contains the names of the module's
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attributes.
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* If the object is a type or class object, the list contains the names of its
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attributes, and recursively of the attributes of its bases.
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* Otherwise, the list contains the object's attributes' names, the names of its
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class's attributes, and recursively of the attributes of its class's base
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classes.
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The resulting list is sorted alphabetically. For example:
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>>> import struct
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>>> dir() # show the names in the module namespace
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['__builtins__', '__name__', 'struct']
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>>> dir(struct) # show the names in the struct module # doctest: +SKIP
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['Struct', '__all__', '__builtins__', '__cached__', '__doc__', '__file__',
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'__initializing__', '__loader__', '__name__', '__package__',
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'_clearcache', 'calcsize', 'error', 'pack', 'pack_into',
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'unpack', 'unpack_from']
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>>> class Shape:
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... def __dir__(self):
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... return ['area', 'perimeter', 'location']
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>>> s = Shape()
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>>> dir(s)
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['area', 'location', 'perimeter']
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.. note::
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Because :func:`dir` is supplied primarily as a convenience for use at an
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interactive prompt, it tries to supply an interesting set of names more
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than it tries to supply a rigorously or consistently defined set of names,
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and its detailed behavior may change across releases. For example,
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metaclass attributes are not in the result list when the argument is a
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class.
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.. function:: divmod(a, b)
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Take two (non complex) numbers as arguments and return a pair of numbers
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consisting of their quotient and remainder when using integer division. With
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mixed operand types, the rules for binary arithmetic operators apply. For
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integers, the result is the same as ``(a // b, a % b)``. For floating point
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numbers the result is ``(q, a % b)``, where *q* is usually ``math.floor(a /
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b)`` but may be 1 less than that. In any case ``q * b + a % b`` is very
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close to *a*, if ``a % b`` is non-zero it has the same sign as *b*, and ``0
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<= abs(a % b) < abs(b)``.
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.. function:: enumerate(iterable, start=0)
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Return an enumerate object. *iterable* must be a sequence, an
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:term:`iterator`, or some other object which supports iteration.
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The :meth:`~iterator.__next__` method of the iterator returned by
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:func:`enumerate` returns a tuple containing a count (from *start* which
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defaults to 0) and the values obtained from iterating over *iterable*.
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>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
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>>> list(enumerate(seasons))
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[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]
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>>> list(enumerate(seasons, start=1))
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[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]
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Equivalent to::
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def enumerate(sequence, start=0):
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n = start
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for elem in sequence:
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yield n, elem
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n += 1
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.. function:: eval(expression, globals=None, locals=None)
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The arguments are a string and optional globals and locals. If provided,
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*globals* must be a dictionary. If provided, *locals* can be any mapping
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object.
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The *expression* argument is parsed and evaluated as a Python expression
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(technically speaking, a condition list) using the *globals* and *locals*
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dictionaries as global and local namespace. If the *globals* dictionary is
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present and lacks '__builtins__', the current globals are copied into *globals*
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before *expression* is parsed. This means that *expression* normally has full
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access to the standard :mod:`builtins` module and restricted environments are
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propagated. If the *locals* dictionary is omitted it defaults to the *globals*
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dictionary. If both dictionaries are omitted, the expression is executed in the
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environment where :func:`eval` is called. The return value is the result of
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the evaluated expression. Syntax errors are reported as exceptions. Example:
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>>> x = 1
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>>> eval('x+1')
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2
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This function can also be used to execute arbitrary code objects (such as
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those created by :func:`compile`). In this case pass a code object instead
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of a string. If the code object has been compiled with ``'exec'`` as the
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*mode* argument, :func:`eval`\'s return value will be ``None``.
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Hints: dynamic execution of statements is supported by the :func:`exec`
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function. The :func:`globals` and :func:`locals` functions
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returns the current global and local dictionary, respectively, which may be
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useful to pass around for use by :func:`eval` or :func:`exec`.
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See :func:`ast.literal_eval` for a function that can safely evaluate strings
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with expressions containing only literals.
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.. function:: exec(object[, globals[, locals]])
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This function supports dynamic execution of Python code. *object* must be
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either a string or a code object. If it is a string, the string is parsed as
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a suite of Python statements which is then executed (unless a syntax error
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occurs). [#]_ If it is a code object, it is simply executed. In all cases,
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the code that's executed is expected to be valid as file input (see the
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section "File input" in the Reference Manual). Be aware that the
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:keyword:`return` and :keyword:`yield` statements may not be used outside of
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function definitions even within the context of code passed to the
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:func:`exec` function. The return value is ``None``.
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In all cases, if the optional parts are omitted, the code is executed in the
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current scope. If only *globals* is provided, it must be a dictionary, which
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will be used for both the global and the local variables. If *globals* and
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*locals* are given, they are used for the global and local variables,
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respectively. If provided, *locals* can be any mapping object. Remember
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that at module level, globals and locals are the same dictionary. If exec
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gets two separate objects as *globals* and *locals*, the code will be
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executed as if it were embedded in a class definition.
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If the *globals* dictionary does not contain a value for the key
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``__builtins__``, a reference to the dictionary of the built-in module
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:mod:`builtins` is inserted under that key. That way you can control what
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builtins are available to the executed code by inserting your own
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``__builtins__`` dictionary into *globals* before passing it to :func:`exec`.
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.. note::
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The built-in functions :func:`globals` and :func:`locals` return the current
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global and local dictionary, respectively, which may be useful to pass around
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for use as the second and third argument to :func:`exec`.
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.. note::
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The default *locals* act as described for function :func:`locals` below:
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modifications to the default *locals* dictionary should not be attempted.
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Pass an explicit *locals* dictionary if you need to see effects of the
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code on *locals* after function :func:`exec` returns.
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.. function:: filter(function, iterable)
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Construct an iterator from those elements of *iterable* for which *function*
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returns true. *iterable* may be either a sequence, a container which
|
|
supports iteration, or an iterator. If *function* is ``None``, the identity
|
|
function is assumed, that is, all elements of *iterable* that are false are
|
|
removed.
|
|
|
|
Note that ``filter(function, iterable)`` is equivalent to the generator
|
|
expression ``(item for item in iterable if function(item))`` if function is
|
|
not ``None`` and ``(item for item in iterable if item)`` if function is
|
|
``None``.
|
|
|
|
See :func:`itertools.filterfalse` for the complementary function that returns
|
|
elements of *iterable* for which *function* returns false.
|
|
|
|
|
|
.. function:: float([x])
|
|
|
|
.. index::
|
|
single: NaN
|
|
single: Infinity
|
|
|
|
Convert a string or a number to floating point.
|
|
|
|
If the argument is a string, it should contain a decimal number, optionally
|
|
preceded by a sign, and optionally embedded in whitespace. The optional
|
|
sign may be ``'+'`` or ``'-'``; a ``'+'`` sign has no effect on the value
|
|
produced. The argument may also be a string representing a NaN
|
|
(not-a-number), or a positive or negative infinity. More precisely, the
|
|
input must conform to the following grammar after leading and trailing
|
|
whitespace characters are removed:
|
|
|
|
.. productionlist::
|
|
sign: "+" | "-"
|
|
infinity: "Infinity" | "inf"
|
|
nan: "nan"
|
|
numeric_value: `floatnumber` | `infinity` | `nan`
|
|
numeric_string: [`sign`] `numeric_value`
|
|
|
|
Here ``floatnumber`` is the form of a Python floating-point literal,
|
|
described in :ref:`floating`. Case is not significant, so, for example,
|
|
"inf", "Inf", "INFINITY" and "iNfINity" are all acceptable spellings for
|
|
positive infinity.
|
|
|
|
Otherwise, if the argument is an integer or a floating point number, a
|
|
floating point number with the same value (within Python's floating point
|
|
precision) is returned. If the argument is outside the range of a Python
|
|
float, an :exc:`OverflowError` will be raised.
|
|
|
|
For a general Python object ``x``, ``float(x)`` delegates to
|
|
``x.__float__()``.
|
|
|
|
If no argument is given, ``0.0`` is returned.
|
|
|
|
Examples::
|
|
|
|
>>> float('+1.23')
|
|
1.23
|
|
>>> float(' -12345\n')
|
|
-12345.0
|
|
>>> float('1e-003')
|
|
0.001
|
|
>>> float('+1E6')
|
|
1000000.0
|
|
>>> float('-Infinity')
|
|
-inf
|
|
|
|
The float type is described in :ref:`typesnumeric`.
|
|
|
|
.. index::
|
|
single: __format__
|
|
single: string; format() (built-in function)
|
|
|
|
|
|
.. function:: format(value[, format_spec])
|
|
|
|
Convert a *value* to a "formatted" representation, as controlled by
|
|
*format_spec*. The interpretation of *format_spec* will depend on the type
|
|
of the *value* argument, however there is a standard formatting syntax that
|
|
is used by most built-in types: :ref:`formatspec`.
|
|
|
|
The default *format_spec* is an empty string which usually gives the same
|
|
effect as calling :func:`str(value) <str>`.
|
|
|
|
A call to ``format(value, format_spec)`` is translated to
|
|
``type(value).__format__(format_spec)`` which bypasses the instance
|
|
dictionary when searching for the value's :meth:`__format__` method. A
|
|
:exc:`TypeError` exception is raised if the method search reaches
|
|
:mod:`object` and the *format_spec* is non-empty, or if either the
|
|
*format_spec* or the return value are not strings.
|
|
|
|
.. versionchanged:: 3.4
|
|
``object().__format__(format_spec)`` raises :exc:`TypeError`
|
|
if *format_spec* is not an empty string.
|
|
|
|
|
|
.. _func-frozenset:
|
|
.. function:: frozenset([iterable])
|
|
:noindex:
|
|
|
|
Return a new :class:`frozenset` object, optionally with elements taken from
|
|
*iterable*. ``frozenset`` is a built-in class. See :class:`frozenset` and
|
|
:ref:`types-set` for documentation about this class.
|
|
|
|
For other containers see the built-in :class:`set`, :class:`list`,
|
|
:class:`tuple`, and :class:`dict` classes, as well as the :mod:`collections`
|
|
module.
|
|
|
|
|
|
.. function:: getattr(object, name[, default])
|
|
|
|
Return the value of the named attribute of *object*. *name* must be a string.
|
|
If the string is the name of one of the object's attributes, the result is the
|
|
value of that attribute. For example, ``getattr(x, 'foobar')`` is equivalent to
|
|
``x.foobar``. If the named attribute does not exist, *default* is returned if
|
|
provided, otherwise :exc:`AttributeError` is raised.
|
|
|
|
|
|
.. function:: globals()
|
|
|
|
Return a dictionary representing the current global symbol table. This is always
|
|
the dictionary of the current module (inside a function or method, this is the
|
|
module where it is defined, not the module from which it is called).
|
|
|
|
|
|
.. function:: hasattr(object, name)
|
|
|
|
The arguments are an object and a string. The result is ``True`` if the
|
|
string is the name of one of the object's attributes, ``False`` if not. (This
|
|
is implemented by calling ``getattr(object, name)`` and seeing whether it
|
|
raises an :exc:`AttributeError` or not.)
|
|
|
|
|
|
.. function:: hash(object)
|
|
|
|
Return the hash value of the object (if it has one). Hash values are
|
|
integers. They are used to quickly compare dictionary keys during a
|
|
dictionary lookup. Numeric values that compare equal have the same hash
|
|
value (even if they are of different types, as is the case for 1 and 1.0).
|
|
|
|
.. note::
|
|
|
|
For object's with custom :meth:`__hash__` methods, note that :func:`hash`
|
|
truncates the return value based on the bit width of the host machine.
|
|
See :meth:`__hash__` for details.
|
|
|
|
.. function:: help([object])
|
|
|
|
Invoke the built-in help system. (This function is intended for interactive
|
|
use.) If no argument is given, the interactive help system starts on the
|
|
interpreter console. If the argument is a string, then the string is looked up
|
|
as the name of a module, function, class, method, keyword, or documentation
|
|
topic, and a help page is printed on the console. If the argument is any other
|
|
kind of object, a help page on the object is generated.
|
|
|
|
This function is added to the built-in namespace by the :mod:`site` module.
|
|
|
|
.. versionchanged:: 3.4
|
|
Changes to :mod:`pydoc` and :mod:`inspect` mean that the reported
|
|
signatures for callables are now more comprehensive and consistent.
|
|
|
|
|
|
.. function:: hex(x)
|
|
|
|
Convert an integer number to a hexadecimal string. The result is a valid Python
|
|
expression. If *x* is not a Python :class:`int` object, it has to define an
|
|
:meth:`__index__` method that returns an integer.
|
|
|
|
.. note::
|
|
|
|
To obtain a hexadecimal string representation for a float, use the
|
|
:meth:`float.hex` method.
|
|
|
|
|
|
.. function:: id(object)
|
|
|
|
Return the "identity" of an object. This is an integer which
|
|
is guaranteed to be unique and constant for this object during its lifetime.
|
|
Two objects with non-overlapping lifetimes may have the same :func:`id`
|
|
value.
|
|
|
|
.. impl-detail:: This is the address of the object in memory.
|
|
|
|
|
|
.. function:: input([prompt])
|
|
|
|
If the *prompt* argument is present, it is written to standard output without
|
|
a trailing newline. The function then reads a line from input, converts it
|
|
to a string (stripping a trailing newline), and returns that. When EOF is
|
|
read, :exc:`EOFError` is raised. Example::
|
|
|
|
>>> s = input('--> ') # doctest: +SKIP
|
|
--> Monty Python's Flying Circus
|
|
>>> s # doctest: +SKIP
|
|
"Monty Python's Flying Circus"
|
|
|
|
If the :mod:`readline` module was loaded, then :func:`input` will use it
|
|
to provide elaborate line editing and history features.
|
|
|
|
|
|
.. function:: int(x=0)
|
|
int(x, base=10)
|
|
|
|
Convert a number or string *x* to an integer, or return ``0`` if no
|
|
arguments are given. If *x* is a number, return :meth:`x.__int__()
|
|
<object.__int__>`. For floating point numbers, this truncates towards zero.
|
|
|
|
If *x* is not a number or if *base* is given, then *x* must be a string,
|
|
:class:`bytes`, or :class:`bytearray` instance representing an :ref:`integer
|
|
literal <integers>` in radix *base*. Optionally, the literal can be
|
|
preceded by ``+`` or ``-`` (with no space in between) and surrounded by
|
|
whitespace. A base-n literal consists of the digits 0 to n-1, with ``a``
|
|
to ``z`` (or ``A`` to ``Z``) having
|
|
values 10 to 35. The default *base* is 10. The allowed values are 0 and 2-36.
|
|
Base-2, -8, and -16 literals can be optionally prefixed with ``0b``/``0B``,
|
|
``0o``/``0O``, or ``0x``/``0X``, as with integer literals in code. Base 0
|
|
means to interpret exactly as a code literal, so that the actual base is 2,
|
|
8, 10, or 16, and so that ``int('010', 0)`` is not legal, while
|
|
``int('010')`` is, as well as ``int('010', 8)``.
|
|
|
|
The integer type is described in :ref:`typesnumeric`.
|
|
|
|
.. versionchanged:: 3.4
|
|
If *base* is not an instance of :class:`int` and the *base* object has a
|
|
:meth:`base.__index__ <object.__index__>` method, that method is called
|
|
to obtain an integer for the base. Previous versions used
|
|
:meth:`base.__int__ <object.__int__>` instead of :meth:`base.__index__
|
|
<object.__index__>`.
|
|
|
|
.. function:: isinstance(object, classinfo)
|
|
|
|
Return true if the *object* argument is an instance of the *classinfo*
|
|
argument, or of a (direct, indirect or :term:`virtual <abstract base
|
|
class>`) subclass thereof. If *object* is not
|
|
an object of the given type, the function always returns false. If
|
|
*classinfo* is not a class (type object), it may be a tuple of type objects,
|
|
or may recursively contain other such tuples (other sequence types are not
|
|
accepted). If *classinfo* is not a type or tuple of types and such tuples,
|
|
a :exc:`TypeError` exception is raised.
|
|
|
|
|
|
.. function:: issubclass(class, classinfo)
|
|
|
|
Return true if *class* is a subclass (direct, indirect or :term:`virtual
|
|
<abstract base class>`) of *classinfo*. A
|
|
class is considered a subclass of itself. *classinfo* may be a tuple of class
|
|
objects, in which case every entry in *classinfo* will be checked. In any other
|
|
case, a :exc:`TypeError` exception is raised.
|
|
|
|
|
|
.. function:: iter(object[, sentinel])
|
|
|
|
Return an :term:`iterator` object. The first argument is interpreted very
|
|
differently depending on the presence of the second argument. Without a
|
|
second argument, *object* must be a collection object which supports the
|
|
iteration protocol (the :meth:`__iter__` method), or it must support the
|
|
sequence protocol (the :meth:`__getitem__` method with integer arguments
|
|
starting at ``0``). If it does not support either of those protocols,
|
|
:exc:`TypeError` is raised. If the second argument, *sentinel*, is given,
|
|
then *object* must be a callable object. The iterator created in this case
|
|
will call *object* with no arguments for each call to its
|
|
:meth:`~iterator.__next__` method; if the value returned is equal to
|
|
*sentinel*, :exc:`StopIteration` will be raised, otherwise the value will
|
|
be returned.
|
|
|
|
See also :ref:`typeiter`.
|
|
|
|
One useful application of the second form of :func:`iter` is to read lines of
|
|
a file until a certain line is reached. The following example reads a file
|
|
until the :meth:`~io.TextIOBase.readline` method returns an empty string::
|
|
|
|
with open('mydata.txt') as fp:
|
|
for line in iter(fp.readline, ''):
|
|
process_line(line)
|
|
|
|
|
|
.. function:: len(s)
|
|
|
|
Return the length (the number of items) of an object. The argument may be a
|
|
sequence (string, tuple or list) or a mapping (dictionary).
|
|
|
|
|
|
.. _func-list:
|
|
.. function:: list([iterable])
|
|
:noindex:
|
|
|
|
Rather than being a function, :class:`list` is actually a mutable
|
|
sequence type, as documented in :ref:`typesseq-list` and :ref:`typesseq`.
|
|
|
|
|
|
.. function:: locals()
|
|
|
|
Update and return a dictionary representing the current local symbol table.
|
|
Free variables are returned by :func:`locals` when it is called in function
|
|
blocks, but not in class blocks.
|
|
|
|
.. note::
|
|
The contents of this dictionary should not be modified; changes may not
|
|
affect the values of local and free variables used by the interpreter.
|
|
|
|
.. function:: map(function, iterable, ...)
|
|
|
|
Return an iterator that applies *function* to every item of *iterable*,
|
|
yielding the results. If additional *iterable* arguments are passed,
|
|
*function* must take that many arguments and is applied to the items from all
|
|
iterables in parallel. With multiple iterables, the iterator stops when the
|
|
shortest iterable is exhausted. For cases where the function inputs are
|
|
already arranged into argument tuples, see :func:`itertools.starmap`\.
|
|
|
|
|
|
.. function:: max(iterable, *[, default, key])
|
|
max(arg1, arg2, *args[, key])
|
|
|
|
Return the largest item in an iterable or the largest of two or more
|
|
arguments.
|
|
|
|
If one positional argument is provided, it should be an :term:`iterable`.
|
|
The largest item in the iterable is returned. If two or more positional
|
|
arguments are provided, the smallest of the positional arguments is
|
|
returned.
|
|
|
|
There are two optional keyword-only arguments. The *key* argument specifies
|
|
a one-argument ordering function like that used for :meth:`list.sort`. The
|
|
*default* argument specifies an object to return if the provided iterable is
|
|
empty. If the iterable is empty and *default* is not provided, a
|
|
:exc:`ValueError` is raised.
|
|
|
|
If multiple items are maximal, the function returns the first one
|
|
encountered. This is consistent with other sort-stability preserving tools
|
|
such as ``sorted(iterable, key=keyfunc, reverse=True)[0]`` and
|
|
``heapq.nlargest(1, iterable, key=keyfunc)``.
|
|
|
|
.. versionadded:: 3.4
|
|
The *default* keyword-only argument.
|
|
|
|
|
|
.. _func-memoryview:
|
|
.. function:: memoryview(obj)
|
|
:noindex:
|
|
|
|
Return a "memory view" object created from the given argument. See
|
|
:ref:`typememoryview` for more information.
|
|
|
|
|
|
.. function:: min(iterable, *[, default, key])
|
|
min(arg1, arg2, *args[, key])
|
|
|
|
Return the smallest item in an iterable or the smallest of two or more
|
|
arguments.
|
|
|
|
If one positional argument is provided, it should be an :term:`iterable`.
|
|
The smallest item in the iterable is returned. If two or more positional
|
|
arguments are provided, the smallest of the positional arguments is
|
|
returned.
|
|
|
|
There are two optional keyword-only arguments. The *key* argument specifies
|
|
a one-argument ordering function like that used for :meth:`list.sort`. The
|
|
*default* argument specifies an object to return if the provided iterable is
|
|
empty. If the iterable is empty and *default* is not provided, a
|
|
:exc:`ValueError` is raised.
|
|
|
|
If multiple items are minimal, the function returns the first one
|
|
encountered. This is consistent with other sort-stability preserving tools
|
|
such as ``sorted(iterable, key=keyfunc)[0]`` and ``heapq.nsmallest(1,
|
|
iterable, key=keyfunc)``.
|
|
|
|
.. versionadded:: 3.4
|
|
The *default* keyword-only argument.
|
|
|
|
.. function:: next(iterator[, default])
|
|
|
|
Retrieve the next item from the *iterator* by calling its
|
|
:meth:`~iterator.__next__` method. If *default* is given, it is returned
|
|
if the iterator is exhausted, otherwise :exc:`StopIteration` is raised.
|
|
|
|
|
|
.. function:: object()
|
|
|
|
Return a new featureless object. :class:`object` is a base for all classes.
|
|
It has the methods that are common to all instances of Python classes. This
|
|
function does not accept any arguments.
|
|
|
|
.. note::
|
|
|
|
:class:`object` does *not* have a :attr:`~object.__dict__`, so you can't
|
|
assign arbitrary attributes to an instance of the :class:`object` class.
|
|
|
|
|
|
.. function:: oct(x)
|
|
|
|
Convert an integer number to an octal string. The result is a valid Python
|
|
expression. If *x* is not a Python :class:`int` object, it has to define an
|
|
:meth:`__index__` method that returns an integer.
|
|
|
|
|
|
.. index::
|
|
single: file object; open() built-in function
|
|
|
|
.. function:: open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)
|
|
|
|
Open *file* and return a corresponding :term:`file object`. If the file
|
|
cannot be opened, an :exc:`OSError` is raised.
|
|
|
|
*file* is either a string or bytes object giving the pathname (absolute or
|
|
relative to the current working directory) of the file to be opened or
|
|
an integer file descriptor of the file to be wrapped. (If a file descriptor
|
|
is given, it is closed when the returned I/O object is closed, unless
|
|
*closefd* is set to ``False``.)
|
|
|
|
*mode* is an optional string that specifies the mode in which the file is
|
|
opened. It defaults to ``'r'`` which means open for reading in text mode.
|
|
Other common values are ``'w'`` for writing (truncating the file if it
|
|
already exists), ``'x'`` for exclusive creation and ``'a'`` for appending
|
|
(which on *some* Unix systems, means that *all* writes append to the end of
|
|
the file regardless of the current seek position). In text mode, if
|
|
*encoding* is not specified the encoding used is platform dependent:
|
|
``locale.getpreferredencoding(False)`` is called to get the current locale
|
|
encoding. (For reading and writing raw bytes use binary mode and leave
|
|
*encoding* unspecified.) The available modes are:
|
|
|
|
========= ===============================================================
|
|
Character Meaning
|
|
========= ===============================================================
|
|
``'r'`` open for reading (default)
|
|
``'w'`` open for writing, truncating the file first
|
|
``'x'`` open for exclusive creation, failing if the file already exists
|
|
``'a'`` open for writing, appending to the end of the file if it exists
|
|
``'b'`` binary mode
|
|
``'t'`` text mode (default)
|
|
``'+'`` open a disk file for updating (reading and writing)
|
|
``'U'`` :term:`universal newlines` mode (deprecated)
|
|
========= ===============================================================
|
|
|
|
The default mode is ``'r'`` (open for reading text, synonym of ``'rt'``).
|
|
For binary read-write access, the mode ``'w+b'`` opens and truncates the file
|
|
to 0 bytes. ``'r+b'`` opens the file without truncation.
|
|
|
|
As mentioned in the :ref:`io-overview`, Python distinguishes between binary
|
|
and text I/O. Files opened in binary mode (including ``'b'`` in the *mode*
|
|
argument) return contents as :class:`bytes` objects without any decoding. In
|
|
text mode (the default, or when ``'t'`` is included in the *mode* argument),
|
|
the contents of the file are returned as :class:`str`, the bytes having been
|
|
first decoded using a platform-dependent encoding or using the specified
|
|
*encoding* if given.
|
|
|
|
.. note::
|
|
|
|
Python doesn't depend on the underlying operating system's notion of text
|
|
files; all the processing is done by Python itself, and is therefore
|
|
platform-independent.
|
|
|
|
*buffering* is an optional integer used to set the buffering policy. Pass 0
|
|
to switch buffering off (only allowed in binary mode), 1 to select line
|
|
buffering (only usable in text mode), and an integer > 1 to indicate the size
|
|
in bytes of a fixed-size chunk buffer. When no *buffering* argument is
|
|
given, the default buffering policy works as follows:
|
|
|
|
* Binary files are buffered in fixed-size chunks; the size of the buffer is
|
|
chosen using a heuristic trying to determine the underlying device's "block
|
|
size" and falling back on :attr:`io.DEFAULT_BUFFER_SIZE`. On many systems,
|
|
the buffer will typically be 4096 or 8192 bytes long.
|
|
|
|
* "Interactive" text files (files for which :meth:`~io.IOBase.isatty`
|
|
returns ``True``) use line buffering. Other text files use the policy
|
|
described above for binary files.
|
|
|
|
*encoding* is the name of the encoding used to decode or encode the file.
|
|
This should only be used in text mode. The default encoding is platform
|
|
dependent (whatever :func:`locale.getpreferredencoding` returns), but any
|
|
encoding supported by Python can be used. See the :mod:`codecs` module for
|
|
the list of supported encodings.
|
|
|
|
*errors* is an optional string that specifies how encoding and decoding
|
|
errors are to be handled--this cannot be used in binary mode.
|
|
A variety of standard error handlers are available, though any
|
|
error handling name that has been registered with
|
|
:func:`codecs.register_error` is also valid. The standard names
|
|
are:
|
|
|
|
* ``'strict'`` to raise a :exc:`ValueError` exception if there is
|
|
an encoding error. The default value of ``None`` has the same
|
|
effect.
|
|
|
|
* ``'ignore'`` ignores errors. Note that ignoring encoding errors
|
|
can lead to data loss.
|
|
|
|
* ``'replace'`` causes a replacement marker (such as ``'?'``) to be inserted
|
|
where there is malformed data.
|
|
|
|
* ``'surrogateescape'`` will represent any incorrect bytes as code
|
|
points in the Unicode Private Use Area ranging from U+DC80 to
|
|
U+DCFF. These private code points will then be turned back into
|
|
the same bytes when the ``surrogateescape`` error handler is used
|
|
when writing data. This is useful for processing files in an
|
|
unknown encoding.
|
|
|
|
* ``'xmlcharrefreplace'`` is only supported when writing to a file.
|
|
Characters not supported by the encoding are replaced with the
|
|
appropriate XML character reference ``&#nnn;``.
|
|
|
|
* ``'backslashreplace'`` (also only supported when writing)
|
|
replaces unsupported characters with Python's backslashed escape
|
|
sequences.
|
|
|
|
.. index::
|
|
single: universal newlines; open() built-in function
|
|
|
|
*newline* controls how :term:`universal newlines` mode works (it only
|
|
applies to text mode). It can be ``None``, ``''``, ``'\n'``, ``'\r'``, and
|
|
``'\r\n'``. It works as follows:
|
|
|
|
* When reading input from the stream, if *newline* is ``None``, universal
|
|
newlines mode is enabled. Lines in the input can end in ``'\n'``,
|
|
``'\r'``, or ``'\r\n'``, and these are translated into ``'\n'`` before
|
|
being returned to the caller. If it is ``''``, universal newlines mode is
|
|
enabled, but line endings are returned to the caller untranslated. If it
|
|
has any of the other legal values, input lines are only terminated by the
|
|
given string, and the line ending is returned to the caller untranslated.
|
|
|
|
* When writing output to the stream, if *newline* is ``None``, any ``'\n'``
|
|
characters written are translated to the system default line separator,
|
|
:data:`os.linesep`. If *newline* is ``''`` or ``'\n'``, no translation
|
|
takes place. If *newline* is any of the other legal values, any ``'\n'``
|
|
characters written are translated to the given string.
|
|
|
|
If *closefd* is ``False`` and a file descriptor rather than a filename was
|
|
given, the underlying file descriptor will be kept open when the file is
|
|
closed. If a filename is given *closefd* has no effect and must be ``True``
|
|
(the default).
|
|
|
|
A custom opener can be used by passing a callable as *opener*. The underlying
|
|
file descriptor for the file object is then obtained by calling *opener* with
|
|
(*file*, *flags*). *opener* must return an open file descriptor (passing
|
|
:mod:`os.open` as *opener* results in functionality similar to passing
|
|
``None``).
|
|
|
|
The newly created file is :ref:`non-inheritable <fd_inheritance>`.
|
|
|
|
The following example uses the :ref:`dir_fd <dir_fd>` parameter of the
|
|
:func:`os.open` function to open a file relative to a given directory::
|
|
|
|
>>> import os
|
|
>>> dir_fd = os.open('somedir', os.O_RDONLY)
|
|
>>> def opener(path, flags):
|
|
... return os.open(path, flags, dir_fd=dir_fd)
|
|
...
|
|
>>> with open('spamspam.txt', 'w', opener=opener) as f:
|
|
... print('This will be written to somedir/spamspam.txt', file=f)
|
|
...
|
|
>>> os.close(dir_fd) # don't leak a file descriptor
|
|
|
|
The type of :term:`file object` returned by the :func:`open` function
|
|
depends on the mode. When :func:`open` is used to open a file in a text
|
|
mode (``'w'``, ``'r'``, ``'wt'``, ``'rt'``, etc.), it returns a subclass of
|
|
:class:`io.TextIOBase` (specifically :class:`io.TextIOWrapper`). When used
|
|
to open a file in a binary mode with buffering, the returned class is a
|
|
subclass of :class:`io.BufferedIOBase`. The exact class varies: in read
|
|
binary mode, it returns a :class:`io.BufferedReader`; in write binary and
|
|
append binary modes, it returns a :class:`io.BufferedWriter`, and in
|
|
read/write mode, it returns a :class:`io.BufferedRandom`. When buffering is
|
|
disabled, the raw stream, a subclass of :class:`io.RawIOBase`,
|
|
:class:`io.FileIO`, is returned.
|
|
|
|
.. index::
|
|
single: line-buffered I/O
|
|
single: unbuffered I/O
|
|
single: buffer size, I/O
|
|
single: I/O control; buffering
|
|
single: binary mode
|
|
single: text mode
|
|
module: sys
|
|
|
|
See also the file handling modules, such as, :mod:`fileinput`, :mod:`io`
|
|
(where :func:`open` is declared), :mod:`os`, :mod:`os.path`, :mod:`tempfile`,
|
|
and :mod:`shutil`.
|
|
|
|
.. versionchanged:: 3.3
|
|
The *opener* parameter was added.
|
|
The ``'x'`` mode was added.
|
|
:exc:`IOError` used to be raised, it is now an alias of :exc:`OSError`.
|
|
:exc:`FileExistsError` is now raised if the file opened in exclusive
|
|
creation mode (``'x'``) already exists.
|
|
|
|
.. versionchanged:: 3.4
|
|
The file is now non-inheritable.
|
|
|
|
.. deprecated-removed:: 3.4 4.0
|
|
The ``'U'`` mode.
|
|
|
|
|
|
.. XXX works for bytes too, but should it?
|
|
.. function:: ord(c)
|
|
|
|
Given a string representing one Unicode character, return an integer
|
|
representing the Unicode code
|
|
point of that character. For example, ``ord('a')`` returns the integer ``97``
|
|
and ``ord('\u2020')`` returns ``8224``. This is the inverse of :func:`chr`.
|
|
|
|
|
|
.. function:: pow(x, y[, z])
|
|
|
|
Return *x* to the power *y*; if *z* is present, return *x* to the power *y*,
|
|
modulo *z* (computed more efficiently than ``pow(x, y) % z``). The two-argument
|
|
form ``pow(x, y)`` is equivalent to using the power operator: ``x**y``.
|
|
|
|
The arguments must have numeric types. With mixed operand types, the
|
|
coercion rules for binary arithmetic operators apply. For :class:`int`
|
|
operands, the result has the same type as the operands (after coercion)
|
|
unless the second argument is negative; in that case, all arguments are
|
|
converted to float and a float result is delivered. For example, ``10**2``
|
|
returns ``100``, but ``10**-2`` returns ``0.01``. If the second argument is
|
|
negative, the third argument must be omitted. If *z* is present, *x* and *y*
|
|
must be of integer types, and *y* must be non-negative.
|
|
|
|
|
|
.. function:: print(*objects, sep=' ', end='\\n', file=sys.stdout, flush=False)
|
|
|
|
Print *objects* to the stream *file*, separated by *sep* and followed by
|
|
*end*. *sep*, *end* and *file*, if present, must be given as keyword
|
|
arguments.
|
|
|
|
All non-keyword arguments are converted to strings like :func:`str` does and
|
|
written to the stream, separated by *sep* and followed by *end*. Both *sep*
|
|
and *end* must be strings; they can also be ``None``, which means to use the
|
|
default values. If no *objects* are given, :func:`print` will just write
|
|
*end*.
|
|
|
|
The *file* argument must be an object with a ``write(string)`` method; if it
|
|
is not present or ``None``, :data:`sys.stdout` will be used. Whether output
|
|
is buffered is usually determined by *file*, but if the *flush* keyword
|
|
argument is true, the stream is forcibly flushed.
|
|
|
|
.. versionchanged:: 3.3
|
|
Added the *flush* keyword argument.
|
|
|
|
|
|
.. function:: property(fget=None, fset=None, fdel=None, doc=None)
|
|
|
|
Return a property attribute.
|
|
|
|
*fget* is a function for getting an attribute value, likewise *fset* is a
|
|
function for setting, and *fdel* a function for del'ing, an attribute. Typical
|
|
use is to define a managed attribute ``x``::
|
|
|
|
class C:
|
|
def __init__(self):
|
|
self._x = None
|
|
|
|
def getx(self):
|
|
return self._x
|
|
def setx(self, value):
|
|
self._x = value
|
|
def delx(self):
|
|
del self._x
|
|
x = property(getx, setx, delx, "I'm the 'x' property.")
|
|
|
|
If then *c* is an instance of *C*, ``c.x`` will invoke the getter,
|
|
``c.x = value`` will invoke the setter and ``del c.x`` the deleter.
|
|
|
|
If given, *doc* will be the docstring of the property attribute. Otherwise, the
|
|
property will copy *fget*'s docstring (if it exists). This makes it possible to
|
|
create read-only properties easily using :func:`property` as a :term:`decorator`::
|
|
|
|
class Parrot:
|
|
def __init__(self):
|
|
self._voltage = 100000
|
|
|
|
@property
|
|
def voltage(self):
|
|
"""Get the current voltage."""
|
|
return self._voltage
|
|
|
|
turns the :meth:`voltage` method into a "getter" for a read-only attribute
|
|
with the same name.
|
|
|
|
A property object has :attr:`~property.getter`, :attr:`~property.setter`,
|
|
and :attr:`~property.deleter` methods usable as decorators that create a
|
|
copy of the property with the corresponding accessor function set to the
|
|
decorated function. This is best explained with an example::
|
|
|
|
class C:
|
|
def __init__(self):
|
|
self._x = None
|
|
|
|
@property
|
|
def x(self):
|
|
"""I'm the 'x' property."""
|
|
return self._x
|
|
|
|
@x.setter
|
|
def x(self, value):
|
|
self._x = value
|
|
|
|
@x.deleter
|
|
def x(self):
|
|
del self._x
|
|
|
|
This code is exactly equivalent to the first example. Be sure to give the
|
|
additional functions the same name as the original property (``x`` in this
|
|
case.)
|
|
|
|
The returned property also has the attributes ``fget``, ``fset``, and
|
|
``fdel`` corresponding to the constructor arguments.
|
|
|
|
|
|
.. _func-range:
|
|
.. function:: range(stop)
|
|
range(start, stop[, step])
|
|
:noindex:
|
|
|
|
Rather than being a function, :class:`range` is actually an immutable
|
|
sequence type, as documented in :ref:`typesseq-range` and :ref:`typesseq`.
|
|
|
|
|
|
.. function:: repr(object)
|
|
|
|
Return a string containing a printable representation of an object. For many
|
|
types, this function makes an attempt to return a string that would yield an
|
|
object with the same value when passed to :func:`eval`, otherwise the
|
|
representation is a string enclosed in angle brackets that contains the name
|
|
of the type of the object together with additional information often
|
|
including the name and address of the object. A class can control what this
|
|
function returns for its instances by defining a :meth:`__repr__` method.
|
|
|
|
|
|
.. function:: reversed(seq)
|
|
|
|
Return a reverse :term:`iterator`. *seq* must be an object which has
|
|
a :meth:`__reversed__` method or supports the sequence protocol (the
|
|
:meth:`__len__` method and the :meth:`__getitem__` method with integer
|
|
arguments starting at ``0``).
|
|
|
|
|
|
.. function:: round(number[, ndigits])
|
|
|
|
Return the floating point value *number* rounded to *ndigits* digits after
|
|
the decimal point. If *ndigits* is omitted, it defaults to zero. Delegates
|
|
to ``number.__round__(ndigits)``.
|
|
|
|
For the built-in types supporting :func:`round`, values are rounded to the
|
|
closest multiple of 10 to the power minus *ndigits*; if two multiples are
|
|
equally close, rounding is done toward the even choice (so, for example,
|
|
both ``round(0.5)`` and ``round(-0.5)`` are ``0``, and ``round(1.5)`` is
|
|
``2``). The return value is an integer if called with one argument,
|
|
otherwise of the same type as *number*.
|
|
|
|
.. note::
|
|
|
|
The behavior of :func:`round` for floats can be surprising: for example,
|
|
``round(2.675, 2)`` gives ``2.67`` instead of the expected ``2.68``.
|
|
This is not a bug: it's a result of the fact that most decimal fractions
|
|
can't be represented exactly as a float. See :ref:`tut-fp-issues` for
|
|
more information.
|
|
|
|
|
|
.. _func-set:
|
|
.. function:: set([iterable])
|
|
:noindex:
|
|
|
|
Return a new :class:`set` object, optionally with elements taken from
|
|
*iterable*. ``set`` is a built-in class. See :class:`set` and
|
|
:ref:`types-set` for documentation about this class.
|
|
|
|
For other containers see the built-in :class:`frozenset`, :class:`list`,
|
|
:class:`tuple`, and :class:`dict` classes, as well as the :mod:`collections`
|
|
module.
|
|
|
|
|
|
.. function:: setattr(object, name, value)
|
|
|
|
This is the counterpart of :func:`getattr`. The arguments are an object, a
|
|
string and an arbitrary value. The string may name an existing attribute or a
|
|
new attribute. The function assigns the value to the attribute, provided the
|
|
object allows it. For example, ``setattr(x, 'foobar', 123)`` is equivalent to
|
|
``x.foobar = 123``.
|
|
|
|
|
|
.. function:: slice(stop)
|
|
slice(start, stop[, step])
|
|
|
|
.. index:: single: Numerical Python
|
|
|
|
Return a :term:`slice` object representing the set of indices specified by
|
|
``range(start, stop, step)``. The *start* and *step* arguments default to
|
|
``None``. Slice objects have read-only data attributes :attr:`~slice.start`,
|
|
:attr:`~slice.stop` and :attr:`~slice.step` which merely return the argument
|
|
values (or their default). They have no other explicit functionality;
|
|
however they are used by Numerical Python and other third party extensions.
|
|
Slice objects are also generated when extended indexing syntax is used. For
|
|
example: ``a[start:stop:step]`` or ``a[start:stop, i]``. See
|
|
:func:`itertools.islice` for an alternate version that returns an iterator.
|
|
|
|
|
|
.. function:: sorted(iterable[, key][, reverse])
|
|
|
|
Return a new sorted list from the items in *iterable*.
|
|
|
|
Has two optional arguments which must be specified as keyword arguments.
|
|
|
|
*key* specifies a function of one argument that is used to extract a comparison
|
|
key from each list element: ``key=str.lower``. The default value is ``None``
|
|
(compare the elements directly).
|
|
|
|
*reverse* is a boolean value. If set to ``True``, then the list elements are
|
|
sorted as if each comparison were reversed.
|
|
|
|
Use :func:`functools.cmp_to_key` to convert an old-style *cmp* function to a
|
|
*key* function.
|
|
|
|
For sorting examples and a brief sorting tutorial, see `Sorting HowTo
|
|
<http://wiki.python.org/moin/HowTo/Sorting/>`_\.
|
|
|
|
.. function:: staticmethod(function)
|
|
|
|
Return a static method for *function*.
|
|
|
|
A static method does not receive an implicit first argument. To declare a static
|
|
method, use this idiom::
|
|
|
|
class C:
|
|
@staticmethod
|
|
def f(arg1, arg2, ...): ...
|
|
|
|
The ``@staticmethod`` form is a function :term:`decorator` -- see the
|
|
description of function definitions in :ref:`function` for details.
|
|
|
|
It can be called either on the class (such as ``C.f()``) or on an instance (such
|
|
as ``C().f()``). The instance is ignored except for its class.
|
|
|
|
Static methods in Python are similar to those found in Java or C++. Also see
|
|
:func:`classmethod` for a variant that is useful for creating alternate class
|
|
constructors.
|
|
|
|
For more information on static methods, consult the documentation on the
|
|
standard type hierarchy in :ref:`types`.
|
|
|
|
.. index::
|
|
single: string; str() (built-in function)
|
|
|
|
|
|
.. _func-str:
|
|
.. function:: str(object='')
|
|
str(object=b'', encoding='utf-8', errors='strict')
|
|
:noindex:
|
|
|
|
Return a :class:`str` version of *object*. See :func:`str` for details.
|
|
|
|
``str`` is the built-in string :term:`class`. For general information
|
|
about strings, see :ref:`textseq`.
|
|
|
|
|
|
.. function:: sum(iterable[, start])
|
|
|
|
Sums *start* and the items of an *iterable* from left to right and returns the
|
|
total. *start* defaults to ``0``. The *iterable*'s items are normally numbers,
|
|
and the start value is not allowed to be a string.
|
|
|
|
For some use cases, there are good alternatives to :func:`sum`.
|
|
The preferred, fast way to concatenate a sequence of strings is by calling
|
|
``''.join(sequence)``. To add floating point values with extended precision,
|
|
see :func:`math.fsum`\. To concatenate a series of iterables, consider using
|
|
:func:`itertools.chain`.
|
|
|
|
.. function:: super([type[, object-or-type]])
|
|
|
|
Return a proxy object that delegates method calls to a parent or sibling
|
|
class of *type*. This is useful for accessing inherited methods that have
|
|
been overridden in a class. The search order is same as that used by
|
|
:func:`getattr` except that the *type* itself is skipped.
|
|
|
|
The :attr:`~class.__mro__` attribute of the *type* lists the method
|
|
resolution search order used by both :func:`getattr` and :func:`super`. The
|
|
attribute is dynamic and can change whenever the inheritance hierarchy is
|
|
updated.
|
|
|
|
If the second argument is omitted, the super object returned is unbound. If
|
|
the second argument is an object, ``isinstance(obj, type)`` must be true. If
|
|
the second argument is a type, ``issubclass(type2, type)`` must be true (this
|
|
is useful for classmethods).
|
|
|
|
There are two typical use cases for *super*. In a class hierarchy with
|
|
single inheritance, *super* can be used to refer to parent classes without
|
|
naming them explicitly, thus making the code more maintainable. This use
|
|
closely parallels the use of *super* in other programming languages.
|
|
|
|
The second use case is to support cooperative multiple inheritance in a
|
|
dynamic execution environment. This use case is unique to Python and is
|
|
not found in statically compiled languages or languages that only support
|
|
single inheritance. This makes it possible to implement "diamond diagrams"
|
|
where multiple base classes implement the same method. Good design dictates
|
|
that this method have the same calling signature in every case (because the
|
|
order of calls is determined at runtime, because that order adapts
|
|
to changes in the class hierarchy, and because that order can include
|
|
sibling classes that are unknown prior to runtime).
|
|
|
|
For both use cases, a typical superclass call looks like this::
|
|
|
|
class C(B):
|
|
def method(self, arg):
|
|
super().method(arg) # This does the same thing as:
|
|
# super(C, self).method(arg)
|
|
|
|
Note that :func:`super` is implemented as part of the binding process for
|
|
explicit dotted attribute lookups such as ``super().__getitem__(name)``.
|
|
It does so by implementing its own :meth:`__getattribute__` method for searching
|
|
classes in a predictable order that supports cooperative multiple inheritance.
|
|
Accordingly, :func:`super` is undefined for implicit lookups using statements or
|
|
operators such as ``super()[name]``.
|
|
|
|
Also note that, aside from the zero argument form, :func:`super` is not
|
|
limited to use inside methods. The two argument form specifies the
|
|
arguments exactly and makes the appropriate references. The zero
|
|
argument form only works inside a class definition, as the compiler fills
|
|
in the necessary details to correctly retrieve the class being defined,
|
|
as well as accessing the current instance for ordinary methods.
|
|
|
|
For practical suggestions on how to design cooperative classes using
|
|
:func:`super`, see `guide to using super()
|
|
<http://rhettinger.wordpress.com/2011/05/26/super-considered-super/>`_.
|
|
|
|
|
|
.. _func-tuple:
|
|
.. function:: tuple([iterable])
|
|
:noindex:
|
|
|
|
Rather than being a function, :class:`tuple` is actually an immutable
|
|
sequence type, as documented in :ref:`typesseq-tuple` and :ref:`typesseq`.
|
|
|
|
|
|
.. function:: type(object)
|
|
type(name, bases, dict)
|
|
|
|
.. index:: object: type
|
|
|
|
|
|
With one argument, return the type of an *object*. The return value is a
|
|
type object and generally the same object as returned by
|
|
:attr:`object.__class__ <instance.__class__>`.
|
|
|
|
The :func:`isinstance` built-in function is recommended for testing the type
|
|
of an object, because it takes subclasses into account.
|
|
|
|
|
|
With three arguments, return a new type object. This is essentially a
|
|
dynamic form of the :keyword:`class` statement. The *name* string is the
|
|
class name and becomes the :attr:`~class.__name__` attribute; the *bases*
|
|
tuple itemizes the base classes and becomes the :attr:`~class.__bases__`
|
|
attribute; and the *dict* dictionary is the namespace containing definitions
|
|
for class body and becomes the :attr:`~object.__dict__` attribute. For
|
|
example, the following two statements create identical :class:`type` objects:
|
|
|
|
>>> class X:
|
|
... a = 1
|
|
...
|
|
>>> X = type('X', (object,), dict(a=1))
|
|
|
|
See also :ref:`bltin-type-objects`.
|
|
|
|
|
|
.. function:: vars([object])
|
|
|
|
Return the :attr:`~object.__dict__` attribute for a module, class, instance,
|
|
or any other object with a :attr:`__dict__` attribute.
|
|
|
|
Objects such as modules and instances have an updateable :attr:`__dict__`
|
|
attribute; however, other objects may have write restrictions on their
|
|
:attr:`__dict__` attributes (for example, classes use a
|
|
dictproxy to prevent direct dictionary updates).
|
|
|
|
Without an argument, :func:`vars` acts like :func:`locals`. Note, the
|
|
locals dictionary is only useful for reads since updates to the locals
|
|
dictionary are ignored.
|
|
|
|
|
|
.. function:: zip(*iterables)
|
|
|
|
Make an iterator that aggregates elements from each of the iterables.
|
|
|
|
Returns an iterator of tuples, where the *i*-th tuple contains
|
|
the *i*-th element from each of the argument sequences or iterables. The
|
|
iterator stops when the shortest input iterable is exhausted. With a single
|
|
iterable argument, it returns an iterator of 1-tuples. With no arguments,
|
|
it returns an empty iterator. Equivalent to::
|
|
|
|
def zip(*iterables):
|
|
# zip('ABCD', 'xy') --> Ax By
|
|
sentinel = object()
|
|
iterators = [iter(it) for it in iterables]
|
|
while iterators:
|
|
result = []
|
|
for it in iterators:
|
|
elem = next(it, sentinel)
|
|
if elem is sentinel:
|
|
return
|
|
result.append(elem)
|
|
yield tuple(result)
|
|
|
|
The left-to-right evaluation order of the iterables is guaranteed. This
|
|
makes possible an idiom for clustering a data series into n-length groups
|
|
using ``zip(*[iter(s)]*n)``.
|
|
|
|
:func:`zip` should only be used with unequal length inputs when you don't
|
|
care about trailing, unmatched values from the longer iterables. If those
|
|
values are important, use :func:`itertools.zip_longest` instead.
|
|
|
|
:func:`zip` in conjunction with the ``*`` operator can be used to unzip a
|
|
list::
|
|
|
|
>>> x = [1, 2, 3]
|
|
>>> y = [4, 5, 6]
|
|
>>> zipped = zip(x, y)
|
|
>>> list(zipped)
|
|
[(1, 4), (2, 5), (3, 6)]
|
|
>>> x2, y2 = zip(*zip(x, y))
|
|
>>> x == list(x2) and y == list(y2)
|
|
True
|
|
|
|
|
|
.. function:: __import__(name, globals=None, locals=None, fromlist=(), level=0)
|
|
|
|
.. index::
|
|
statement: import
|
|
module: imp
|
|
|
|
.. note::
|
|
|
|
This is an advanced function that is not needed in everyday Python
|
|
programming, unlike :func:`importlib.import_module`.
|
|
|
|
This function is invoked by the :keyword:`import` statement. It can be
|
|
replaced (by importing the :mod:`builtins` module and assigning to
|
|
``builtins.__import__``) in order to change semantics of the
|
|
:keyword:`import` statement, but doing so is **strongly** discouraged as it
|
|
is usually simpler to use import hooks (see :pep:`302`) to attain the same
|
|
goals and does not cause issues with code which assumes the default import
|
|
implementation is in use. Direct use of :func:`__import__` is also
|
|
discouraged in favor of :func:`importlib.import_module`.
|
|
|
|
The function imports the module *name*, potentially using the given *globals*
|
|
and *locals* to determine how to interpret the name in a package context.
|
|
The *fromlist* gives the names of objects or submodules that should be
|
|
imported from the module given by *name*. The standard implementation does
|
|
not use its *locals* argument at all, and uses its *globals* only to
|
|
determine the package context of the :keyword:`import` statement.
|
|
|
|
*level* specifies whether to use absolute or relative imports. ``0`` (the
|
|
default) means only perform absolute imports. Positive values for
|
|
*level* indicate the number of parent directories to search relative to the
|
|
directory of the module calling :func:`__import__` (see :pep:`328` for the
|
|
details).
|
|
|
|
When the *name* variable is of the form ``package.module``, normally, the
|
|
top-level package (the name up till the first dot) is returned, *not* the
|
|
module named by *name*. However, when a non-empty *fromlist* argument is
|
|
given, the module named by *name* is returned.
|
|
|
|
For example, the statement ``import spam`` results in bytecode resembling the
|
|
following code::
|
|
|
|
spam = __import__('spam', globals(), locals(), [], 0)
|
|
|
|
The statement ``import spam.ham`` results in this call::
|
|
|
|
spam = __import__('spam.ham', globals(), locals(), [], 0)
|
|
|
|
Note how :func:`__import__` returns the toplevel module here because this is
|
|
the object that is bound to a name by the :keyword:`import` statement.
|
|
|
|
On the other hand, the statement ``from spam.ham import eggs, sausage as
|
|
saus`` results in ::
|
|
|
|
_temp = __import__('spam.ham', globals(), locals(), ['eggs', 'sausage'], 0)
|
|
eggs = _temp.eggs
|
|
saus = _temp.sausage
|
|
|
|
Here, the ``spam.ham`` module is returned from :func:`__import__`. From this
|
|
object, the names to import are retrieved and assigned to their respective
|
|
names.
|
|
|
|
If you simply want to import a module (potentially within a package) by name,
|
|
use :func:`importlib.import_module`.
|
|
|
|
.. versionchanged:: 3.3
|
|
Negative values for *level* are no longer supported (which also changes
|
|
the default value to 0).
|
|
|
|
|
|
.. rubric:: Footnotes
|
|
|
|
.. [#] Note that the parser only accepts the Unix-style end of line convention.
|
|
If you are reading the code from a file, make sure to use newline conversion
|
|
mode to convert Windows or Mac-style newlines.
|