diff options
Diffstat (limited to 'Doc/library/functions.rst')
| -rw-r--r-- | Doc/library/functions.rst | 267 |
1 files changed, 112 insertions, 155 deletions
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst index 93d35f8..91d0aaf 100644 --- a/Doc/library/functions.rst +++ b/Doc/library/functions.rst @@ -14,12 +14,12 @@ are always available. They are listed here in alphabetical order. :func:`all` :func:`dir` :func:`hex` :func:`next` :func:`slice` :func:`any` :func:`divmod` :func:`id` :func:`object` :func:`sorted` :func:`ascii` :func:`enumerate` :func:`input` :func:`oct` :func:`staticmethod` -:func:`bin` :func:`eval` :func:`int` :func:`open` :func:`str` +:func:`bin` :func:`eval` :func:`int` :func:`open` |func-str|_ :func:`bool` :func:`exec` :func:`isinstance` :func:`ord` :func:`sum` :func:`bytearray` :func:`filter` :func:`issubclass` :func:`pow` :func:`super` -:func:`bytes` :func:`float` :func:`iter` :func:`print` :func:`tuple` +:func:`bytes` :func:`float` :func:`iter` :func:`print` |func-tuple|_ :func:`callable` :func:`format` :func:`len` :func:`property` :func:`type` -:func:`chr` |func-frozenset|_ :func:`list` :func:`range` :func:`vars` +:func:`chr` |func-frozenset|_ |func-list|_ |func-range|_ :func:`vars` :func:`classmethod` :func:`getattr` :func:`locals` :func:`repr` :func:`zip` :func:`compile` :func:`globals` :func:`map` :func:`reversed` :func:`__import__` :func:`complex` :func:`hasattr` :func:`max` :func:`round` @@ -33,6 +33,10 @@ are always available. They are listed here in alphabetical order. .. |func-frozenset| replace:: ``frozenset()`` .. |func-memoryview| replace:: ``memoryview()`` .. |func-set| replace:: ``set()`` +.. |func-list| replace:: ``list()`` +.. |func-str| replace:: ``str()`` +.. |func-tuple| replace:: ``tuple()`` +.. |func-range| replace:: ``range()`` .. function:: abs(x) @@ -93,6 +97,7 @@ are always available. They are listed here in alphabetical order. .. index:: pair: Boolean; type +.. _func-bytearray: .. function:: bytearray([source[, encoding[, errors]]]) Return a new array of bytes. The :class:`bytearray` type is a mutable @@ -118,7 +123,10 @@ are always available. They are listed here in alphabetical order. Without an argument, an array of size 0 is created. + See also :ref:`binaryseq` and :ref:`typebytearray`. + +.. _func-bytes: .. function:: bytes([source[, encoding[, errors]]]) Return a new "bytes" object, which is an immutable sequence of integers in @@ -130,6 +138,8 @@ are always available. They are listed here in alphabetical order. Bytes objects can also be created with literals, see :ref:`strings`. + See also :ref:`binaryseq`, :ref:`typebytes`, and :ref:`bytes-methods`. + .. function:: callable(object) @@ -152,10 +162,6 @@ are always available. They are listed here in alphabetical order. 1,114,111 (0x10FFFF in base 16). :exc:`ValueError` will be raised if *i* is outside that range. - Note that on narrow Unicode builds, the result is a string of - length two for *i* greater than 65,535 (0xFFFF in hexadecimal). - - .. function:: classmethod(function) @@ -312,17 +318,18 @@ are always available. They are listed here in alphabetical order. >>> import struct >>> dir() # show the names in the module namespace - ['__builtins__', '__doc__', '__name__', 'struct'] - >>> dir(struct) # show the names in the struct module - ['Struct', '__builtins__', '__doc__', '__file__', '__name__', - '__package__', '_clearcache', 'calcsize', 'error', 'pack', 'pack_into', + ['__builtins__', '__name__', 'struct'] + >>> dir(struct) # show the names in the struct module # doctest: +SKIP + ['Struct', '__all__', '__builtins__', '__cached__', '__doc__', '__file__', + '__initializing__', '__loader__', '__name__', '__package__', + '_clearcache', 'calcsize', 'error', 'pack', 'pack_into', 'unpack', 'unpack_from'] >>> class Shape: - def __dir__(self): - return ['area', 'perimeter', 'location'] + ... def __dir__(self): + ... return ['area', 'perimeter', 'location'] >>> s = Shape() >>> dir(s) - ['area', 'perimeter', 'location'] + ['area', 'location', 'perimeter'] .. note:: @@ -515,12 +522,12 @@ are always available. They are listed here in alphabetical order. The float type is described in :ref:`typesnumeric`. - -.. function:: format(value[, format_spec]) - .. index:: - pair: str; format 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 @@ -623,9 +630,9 @@ are always available. They are listed here in alphabetical order. to a string (stripping a trailing newline), and returns that. When EOF is read, :exc:`EOFError` is raised. Example:: - >>> s = input('--> ') + >>> s = input('--> ') # doctest: +SKIP --> Monty Python's Flying Circus - >>> s + >>> s # doctest: +SKIP "Monty Python's Flying Circus" If the :mod:`readline` module was loaded, then :func:`input` will use it @@ -691,6 +698,8 @@ are always available. They are listed here in alphabetical order. *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:`readline` method returns an empty string:: @@ -706,16 +715,12 @@ are always available. They are listed here in alphabetical order. sequence (string, tuple or list) or a mapping (dictionary). +.. _func-list: .. function:: list([iterable]) + :noindex: - Return a list whose items are the same and in the same order as *iterable*'s - items. *iterable* may be either a sequence, a container that supports - iteration, or an iterator object. If *iterable* is already a list, a copy is - made and returned, similar to ``iterable[:]``. For instance, ``list('abc')`` - returns ``['a', 'b', 'c']`` and ``list( (1, 2, 3) )`` returns ``[1, 2, 3]``. - If no argument is given, returns a new empty list, ``[]``. - - :class:`list` is a mutable sequence type, as documented in :ref:`typesseq`. + Rather than being a function, :class:`list` is actually a mutable + sequence type, as documented in :ref:`typesseq-list` and :ref:`typesseq`. .. function:: locals() @@ -814,10 +819,10 @@ are always available. They are listed here in alphabetical order. .. index:: single: file object; open() built-in function -.. function:: open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True) +.. 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:`IOError` is raised. + 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 @@ -828,17 +833,20 @@ are always available. They are listed here in alphabetical order. *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), 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. (For reading and writing raw bytes use - binary mode and leave *encoding* unspecified.) The available modes are: + 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) @@ -924,6 +932,29 @@ are always available. They are listed here in alphabetical order. 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 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 + + .. versionchanged:: 3.3 + The *opener* parameter was added. + The ``'x'`` mode was added. + 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 @@ -949,6 +980,11 @@ are always available. They are listed here in alphabetical order. (where :func:`open` is declared), :mod:`os`, :mod:`os.path`, :mod:`tempfile`, and :mod:`shutil`. + .. versionchanged:: 3.3 + :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. + .. XXX works for bytes too, but should it? .. function:: ord(c) @@ -958,9 +994,6 @@ are always available. They are listed here in alphabetical order. point of that character. For example, ``ord('a')`` returns the integer ``97`` and ``ord('\u2020')`` returns ``8224``. This is the inverse of :func:`chr`. - On wide Unicode builds, if the argument length is not one, a - :exc:`TypeError` will be raised. On narrow Unicode builds, strings - of length two are accepted when they form a UTF-16 surrogate pair. .. function:: pow(x, y[, z]) @@ -978,7 +1011,7 @@ are always available. They are listed here in alphabetical order. must be of integer types, and *y* must be non-negative. -.. function:: print(*objects, sep=' ', end='\\n', file=sys.stdout) +.. 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 @@ -991,9 +1024,12 @@ are always available. They are listed here in alphabetical order. *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. Output buffering - is determined by *file*. Use ``file.flush()`` to ensure, for instance, - immediate appearance on a screen. + 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) @@ -1065,63 +1101,13 @@ are always available. They are listed here in alphabetical order. ``fdel`` corresponding to the constructor arguments. -.. XXX does accept objects with __index__ too +.. _func-range: .. function:: range(stop) range(start, stop[, step]) + :noindex: - This is a versatile function to create iterables yielding arithmetic - progressions. It is most often used in :keyword:`for` loops. The arguments - must be integers. If the *step* argument is omitted, it defaults to ``1``. - If the *start* argument is omitted, it defaults to ``0``. The full form - returns an iterable of integers ``[start, start + step, start + 2 * step, - ...]``. If *step* is positive, the last element is the largest ``start + i * - step`` less than *stop*; if *step* is negative, the last element is the - smallest ``start + i * step`` greater than *stop*. *step* must not be zero - (or else :exc:`ValueError` is raised). Example: - - >>> list(range(10)) - [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] - >>> list(range(1, 11)) - [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] - >>> list(range(0, 30, 5)) - [0, 5, 10, 15, 20, 25] - >>> list(range(0, 10, 3)) - [0, 3, 6, 9] - >>> list(range(0, -10, -1)) - [0, -1, -2, -3, -4, -5, -6, -7, -8, -9] - >>> list(range(0)) - [] - >>> list(range(1, 0)) - [] - - Range objects implement the :class:`collections.Sequence` ABC, and provide - features such as containment tests, element index lookup, slicing and - support for negative indices (see :ref:`typesseq`): - - >>> r = range(0, 20, 2) - >>> r - range(0, 20, 2) - >>> 11 in r - False - >>> 10 in r - True - >>> r.index(10) - 5 - >>> r[5] - 10 - >>> r[:5] - range(0, 10, 2) - >>> r[-1] - 18 - - Ranges containing absolute values larger than :data:`sys.maxsize` are permitted - but some features (such as :func:`len`) will raise :exc:`OverflowError`. - - .. versionchanged:: 3.2 - Implement the Sequence ABC. - Support slicing and negative indices. - Test integers for membership in constant time instead of iterating - through all items. + 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) @@ -1250,47 +1236,15 @@ are always available. They are listed here in alphabetical order. single: string; str() (built-in function) +.. _func-str: .. function:: str(object='') str(object=b'', encoding='utf-8', errors='strict') + :noindex: - Return a :ref:`string <typesseq>` version of *object*. If *object* is not - provided, returns the empty string. Otherwise, the behavior of ``str()`` - depends on whether *encoding* or *errors* is given, as follows. - - If neither *encoding* nor *errors* is given, ``str(object)`` returns - :meth:`object.__str__() <object.__str__>`, which is the "informal" or nicely - printable string representation of *object*. For string objects, this is - the string itself. If *object* does not have a :meth:`~object.__str__` - method, then :func:`str` falls back to returning - :meth:`repr(object) <repr>`. + Return a :class:`str` version of *object*. See :func:`str` for details. - .. index:: - single: buffer protocol; str() (built-in function) - single: bytes; str() (built-in function) - - If at least one of *encoding* or *errors* is given, *object* should be a - :class:`bytes` or :class:`bytearray` object, or more generally any object - that supports the :ref:`buffer protocol <bufferobjects>`. In this case, if - *object* is a :class:`bytes` (or :class:`bytearray`) object, then - ``str(bytes, encoding, errors)`` is equivalent to - :meth:`bytes.decode(encoding, errors) <bytes.decode>`. Otherwise, the bytes - object underlying the buffer object is obtained before calling - :meth:`bytes.decode`. See the :ref:`typesseq` section, the - :ref:`typememoryview` section, and :ref:`bufferobjects` for information on - buffer objects. - - Passing a :class:`bytes` object to :func:`str` without the *encoding* - or *errors* arguments falls under the first case of returning the informal - string representation (see also the :option:`-b` command-line option to - Python). For example:: - - >>> str(b'Zoot!') - "b'Zoot!'" - - ``str`` is a built-in :term:`type`. For more information on the string - type and its methods, see the :ref:`typesseq` and :ref:`string-methods` - sections. To output formatted strings, see the :ref:`string-formatting` - section. In addition, see the :ref:`stringservices` section. + ``str`` is the built-in string :term:`class`. For general information + about strings, see :ref:`textseq`. .. function:: sum(iterable[, start]) @@ -1350,26 +1304,24 @@ are always available. They are listed here in alphabetical order. Accordingly, :func:`super` is undefined for implicit lookups using statements or operators such as ``super()[name]``. - Also note that :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 automatically searches the stack frame - for the class (``__class__``) and the first argument. + 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: - Return a tuple whose items are the same and in the same order as *iterable*'s - items. *iterable* may be a sequence, a container that supports iteration, or an - iterator object. If *iterable* is already a tuple, it is returned unchanged. - For instance, ``tuple('abc')`` returns ``('a', 'b', 'c')`` and ``tuple([1, 2, - 3])`` returns ``(1, 2, 3)``. If no argument is given, returns a new empty - tuple, ``()``. - - :class:`tuple` is an immutable sequence type, as documented in :ref:`typesseq`. + 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) @@ -1398,6 +1350,8 @@ are always available. They are listed here in alphabetical order. ... >>> X = type('X', (object,), dict(a=1)) + See also :ref:`bltin-type-objects`. + .. function:: vars([object]) @@ -1454,7 +1408,7 @@ are always available. They are listed here in alphabetical order. True -.. function:: __import__(name, globals={}, locals={}, fromlist=[], level=-1) +.. function:: __import__(name, globals=None, locals=None, fromlist=(), level=0) .. index:: statement: import @@ -1469,8 +1423,9 @@ are always available. They are listed here in alphabetical order. replaced (by importing the :mod:`builtins` module and assigning to ``builtins.__import__``) in order to change semantics of the :keyword:`import` statement, but nowadays it is usually simpler to use import - hooks (see :pep:`302`). Direct use of :func:`__import__` is rare, except in - cases where you want to import a module whose name is only known at runtime. + hooks (see :pep:`302`) to attain the same goals. Direct use of + :func:`__import__` is entirely 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. @@ -1479,13 +1434,11 @@ are always available. They are listed here in alphabetical order. 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`` - 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__`. Negative values attempt both an implicit - relative import and an absolute import (usage of negative values for *level* - are strongly discouraged as future versions of Python do not support such - values). Import statements only use values of 0 or greater. + *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 @@ -1518,6 +1471,10 @@ are always available. They are listed here in alphabetical order. 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 |