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+
+.. _built-in-funcs:
+
+Built-in Functions
+==================
+
+The Python interpreter has a number of functions built into it that are always
+available. They are listed here in alphabetical order.
+
+
+.. function:: __import__(name[, globals[, locals[, fromlist[, level]]]])
+
+ .. index::
+ statement: import
+ module: ihooks
+ module: rexec
+ module: imp
+
+ .. note::
+
+ This is an advanced function that is not needed in everyday Python
+ programming.
+
+ The function is invoked by the :keyword:`import` statement. It mainly exists
+ so that you can replace it with another function that has a compatible
+ interface, in order to change the semantics of the :keyword:`import` statement.
+ For examples of why and how you would do this, see the standard library modules
+ :mod:`ihooks` and :mod:`rexec`. See also the built-in module :mod:`imp`, which
+ defines some useful operations out of which you can build your own
+ :func:`__import__` function.
+
+ For example, the statement ``import spam`` results in the following call:
+ ``__import__('spam',`` ``globals(),`` ``locals(), [], -1)``; the statement
+ ``from spam.ham import eggs`` results in ``__import__('spam.ham', globals(),
+ locals(), ['eggs'], -1)``. Note that even though ``locals()`` and ``['eggs']``
+ are passed in as arguments, the :func:`__import__` function does not set the
+ local variable named ``eggs``; this is done by subsequent code that is generated
+ for the import statement. (In fact, 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.)
+
+ 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. This is done for
+ compatibility with the bytecode generated for the different kinds of import
+ statement; when using ``import spam.ham.eggs``, the top-level package
+ :mod:`spam` must be placed in the importing namespace, but when using ``from
+ spam.ham import eggs``, the ``spam.ham`` subpackage must be used to find the
+ ``eggs`` variable. As a workaround for this behavior, use :func:`getattr` to
+ extract the desired components. For example, you could define the following
+ helper::
+
+ def my_import(name):
+ mod = __import__(name)
+ components = name.split('.')
+ for comp in components[1:]:
+ mod = getattr(mod, comp)
+ return mod
+
+ *level* specifies whether to use absolute or relative imports. The default is
+ ``-1`` which indicates both absolute and relative imports will be attempted.
+ ``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__`.
+
+ .. versionchanged:: 2.5
+ The level parameter was added.
+
+ .. versionchanged:: 2.5
+ Keyword support for parameters was added.
+
+
+.. function:: abs(x)
+
+ Return the absolute value of a number. The argument may be a plain or long
+ integer or a floating point number. If the argument is a complex number, its
+ magnitude is returned.
+
+
+.. function:: all(iterable)
+
+ Return True if all elements of the *iterable* are true. Equivalent to::
+
+ def all(iterable):
+ for element in iterable:
+ if not element:
+ return False
+ return True
+
+ .. versionadded:: 2.5
+
+
+.. function:: any(iterable)
+
+ Return True if any element of the *iterable* is true. Equivalent to::
+
+ def any(iterable):
+ for element in iterable:
+ if element:
+ return True
+ return False
+
+ .. versionadded:: 2.5
+
+
+.. function:: basestring()
+
+ This abstract type is the superclass for :class:`str` and :class:`unicode`. It
+ cannot be called or instantiated, but it can be used to test whether an object
+ is an instance of :class:`str` or :class:`unicode`. ``isinstance(obj,
+ basestring)`` is equivalent to ``isinstance(obj, (str, unicode))``.
+
+ .. versionadded:: 2.3
+
+
+.. function:: bool([x])
+
+ Convert a value to a Boolean, using the standard truth testing procedure. If
+ *x* is false or omitted, this returns :const:`False`; otherwise it returns
+ :const:`True`. :class:`bool` is also a class, which is a subclass of
+ :class:`int`. Class :class:`bool` cannot be subclassed further. Its only
+ instances are :const:`False` and :const:`True`.
+
+ .. index:: pair: Boolean; type
+
+ .. versionadded:: 2.2.1
+
+ .. versionchanged:: 2.3
+ If no argument is given, this function returns :const:`False`.
+
+
+.. function:: callable(object)
+
+ Return :const:`True` if the *object* argument appears callable,
+ :const:`False` if not. If this
+ returns true, it is still possible that a call fails, but if it is false,
+ calling *object* will never succeed. Note that classes are callable (calling a
+ class returns a new instance); class instances are callable if they have a
+ :meth:`__call__` method.
+
+
+.. function:: chr(i)
+
+ Return a string of one character whose ASCII code is the integer *i*. For
+ example, ``chr(97)`` returns the string ``'a'``. This is the inverse of
+ :func:`ord`. The argument must be in the range [0..255], inclusive;
+ :exc:`ValueError` will be raised if *i* is outside that range. See
+ also :func:`unichr`.
+
+
+.. function:: classmethod(function)
+
+ Return a class method for *function*.
+
+ A class method receives the class as implicit first argument, just like an
+ instance method receives the instance. To declare a class method, use this
+ idiom::
+
+ class C:
+ @classmethod
+ def f(cls, arg1, arg2, ...): ...
+
+ The ``@classmethod`` form is a function 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. If a class
+ method is called for a derived class, the derived class object is passed as the
+ implied first argument.
+
+ Class methods are different than C++ or Java static methods. If you want those,
+ see :func:`staticmethod` in this section.
+
+ For more information on class methods, consult the documentation on the standard
+ type hierarchy in :ref:`types`.
+
+ .. versionadded:: 2.2
+
+ .. versionchanged:: 2.4
+ Function decorator syntax added.
+
+
+.. function:: cmp(x, y)
+
+ Compare the two objects *x* and *y* and return an integer according to the
+ outcome. The return value is negative if ``x < y``, zero if ``x == y`` and
+ strictly positive if ``x > y``.
+
+
+.. function:: compile(source, filename, mode[, flags[, dont_inherit]])
+
+ Compile the *source* into a code object. Code objects can be executed by an
+ :keyword:`exec` statement or evaluated by a call to :func:`eval`. The
+ *filename* argument should give the file from which the code was read; pass some
+ recognizable value if it wasn't read from a file (``'<string>'`` is commonly
+ used). The *mode* argument specifies what kind of code must be compiled; it can
+ be ``'exec'`` if *source* consists of a sequence of statements, ``'eval'`` if it
+ consists of a single expression, or ``'single'`` if it consists of a single
+ interactive statement (in the latter case, expression statements that evaluate
+ to something else than ``None`` will be printed).
+
+ When compiling multi-line statements, two caveats apply: line endings must be
+ represented by a single newline character (``'\n'``), and the input must be
+ terminated by at least one newline character. If line endings are represented
+ by ``'\r\n'``, use the string :meth:`replace` method to change them into
+ ``'\n'``.
+
+ The optional arguments *flags* and *dont_inherit* (which are new in Python 2.2)
+ control which future statements (see :pep:`236`) affect the compilation of
+ *source*. If neither is present (or both are zero) the code is compiled with
+ those future statements that are in effect in the code that is calling compile.
+ If the *flags* argument is given and *dont_inherit* is not (or is zero) then the
+ future statements specified by the *flags* argument are used in addition to
+ those that would be used anyway. If *dont_inherit* is a non-zero integer then
+ the *flags* argument is it -- the future statements in effect around the call to
+ compile are ignored.
+
+ Future statements are specified by bits which can be bitwise or-ed together to
+ specify multiple statements. The bitfield required to specify a given feature
+ can be found as the :attr:`compiler_flag` attribute on the :class:`_Feature`
+ instance in the :mod:`__future__` module.
+
+
+.. function:: complex([real[, imag]])
+
+ Create a complex number with the value *real* + *imag*\*j or convert a string or
+ number to a complex number. If the first parameter is a string, it will be
+ interpreted as a complex number and the function must be called without a second
+ parameter. The second parameter can never be a string. Each argument may be any
+ numeric type (including complex). If *imag* is omitted, it defaults to zero and
+ the function serves as a numeric conversion function like :func:`int`,
+ :func:`long` and :func:`float`. If both arguments are omitted, returns ``0j``.
+
+ The complex type is described in :ref:`typesnumeric`.
+
+
+.. function:: delattr(object, name)
+
+ This is a relative of :func:`setattr`. The arguments are an object and a
+ string. The string must be the name of one of the object's attributes. The
+ function deletes the named attribute, provided the object allows it. For
+ example, ``delattr(x, 'foobar')`` is equivalent to ``del x.foobar``.
+
+
+.. function:: dict([arg])
+ :noindex:
+
+ Create a new data dictionary, optionally with items taken from *arg*.
+ The dictionary type is described in :ref:`typesmapping`.
+
+ For other containers see the built in :class:`list`, :class:`set`, and
+ :class:`tuple` classes, and the :mod:`collections` module.
+
+
+.. function:: dir([object])
+
+ Without arguments, return the list of names in the current local scope. With an
+ argument, attempt to return a list of valid attributes for that object.
+
+ If the object has a method named :meth:`__dir__`, this method will be called and
+ must return the list of attributes. This allows objects that implement a custom
+ :func:`__getattr__` or :func:`__getattribute__` function to customize the way
+ :func:`dir` reports their attributes.
+
+ If the object does not provide :meth:`__dir__`, the function tries its best to
+ gather information from the object's :attr:`__dict__` attribute, if defined, and
+ from its type object. The resulting list is not necessarily complete, and may
+ be inaccurate when the object has a custom :func:`__getattr__`.
+
+ The default :func:`dir` mechanism behaves differently with different types of
+ objects, as it attempts to produce the most relevant, rather than complete,
+ information:
+
+ * If the object is a module object, the list contains the names of the module's
+ attributes.
+
+ * If the object is a type or class object, the list contains the names of its
+ attributes, and recursively of the attributes of its bases.
+
+ * Otherwise, the list contains the object's attributes' names, the names of its
+ class's attributes, and recursively of the attributes of its class's base
+ classes.
+
+ The resulting list is sorted alphabetically. For example::
+
+ >>> import struct
+ >>> dir()
+ ['__builtins__', '__doc__', '__name__', 'struct']
+ >>> dir(struct)
+ ['__doc__', '__name__', 'calcsize', 'error', 'pack', 'unpack']
+ >>> class Foo(object):
+ ... def __dir__(self):
+ ... return ["kan", "ga", "roo"]
+ ...
+ >>> f = Foo()
+ >>> dir(f)
+ ['ga', 'kan', 'roo']
+
+ .. note::
+
+ Because :func:`dir` is supplied primarily as a convenience for use at an
+ interactive prompt, it tries to supply an interesting set of names more than it
+ tries to supply a rigorously or consistently defined set of names, and its
+ detailed behavior may change across releases.
+
+
+.. function:: divmod(a, b)
+
+ Take two (non complex) numbers as arguments and return a pair of numbers
+ consisting of their quotient and remainder when using long division. With mixed
+ operand types, the rules for binary arithmetic operators apply. For plain and
+ long integers, the result is the same as ``(a // b, a % b)``. For floating point
+ numbers the result is ``(q, a % b)``, where *q* is usually ``math.floor(a / b)``
+ but may be 1 less than that. In any case ``q * b + a % b`` is very close to
+ *a*, if ``a % b`` is non-zero it has the same sign as *b*, and ``0 <= abs(a % b)
+ < abs(b)``.
+
+ .. versionchanged:: 2.3
+ Using :func:`divmod` with complex numbers is deprecated.
+
+
+.. function:: enumerate(iterable)
+
+ Return an enumerate object. *iterable* must be a sequence, an iterator, or some
+ other object which supports iteration. The :meth:`next` method of the iterator
+ returned by :func:`enumerate` returns a tuple containing a count (from zero) and
+ the corresponding value obtained from iterating over *iterable*.
+ :func:`enumerate` is useful for obtaining an indexed series: ``(0, seq[0])``,
+ ``(1, seq[1])``, ``(2, seq[2])``, .... For example::
+
+ >>> for i, season in enumerate(['Spring', 'Summer', 'Fall', 'Winter')]:
+ >>> print i, season
+ 0 Spring
+ 1 Summer
+ 2 Fall
+ 3 Winter
+
+ .. versionadded:: 2.3
+
+
+.. function:: eval(expression[, globals[, locals]])
+
+ The arguments are a string and optional globals and locals. If provided,
+ *globals* must be a dictionary. If provided, *locals* can be any mapping
+ object.
+
+ .. versionchanged:: 2.4
+ formerly *locals* was required to be a dictionary.
+
+ The *expression* argument is parsed and evaluated as a Python expression
+ (technically speaking, a condition list) using the *globals* and *locals*
+ dictionaries as global and local name space. If the *globals* dictionary is
+ present and lacks '__builtins__', the current globals are copied into *globals*
+ before *expression* is parsed. This means that *expression* normally has full
+ access to the standard :mod:`__builtin__` module and restricted environments are
+ propagated. If the *locals* dictionary is omitted it defaults to the *globals*
+ dictionary. If both dictionaries are omitted, the expression is executed in the
+ environment where :keyword:`eval` is called. The return value is the result of
+ the evaluated expression. Syntax errors are reported as exceptions. Example::
+
+ >>> x = 1
+ >>> print eval('x+1')
+ 2
+
+ This function can also be used to execute arbitrary code objects (such as those
+ created by :func:`compile`). In this case pass a code object instead of a
+ string. The code object must have been compiled passing ``'eval'`` as the
+ *kind* argument.
+
+ Hints: dynamic execution of statements is supported by the :keyword:`exec`
+ statement. Execution of statements from a file is supported by the
+ :func:`execfile` function. The :func:`globals` and :func:`locals` functions
+ returns the current global and local dictionary, respectively, which may be
+ useful to pass around for use by :func:`eval` or :func:`execfile`.
+
+
+.. function:: execfile(filename[, globals[, locals]])
+
+ This function is similar to the :keyword:`exec` statement, but parses a file
+ instead of a string. It is different from the :keyword:`import` statement in
+ that it does not use the module administration --- it reads the file
+ unconditionally and does not create a new module. [#]_
+
+ The arguments are a file name and two optional dictionaries. The file is parsed
+ and evaluated as a sequence of Python statements (similarly to a module) using
+ the *globals* and *locals* dictionaries as global and local namespace. If
+ provided, *locals* can be any mapping object.
+
+ .. versionchanged:: 2.4
+ formerly *locals* was required to be a dictionary.
+
+ If the *locals* dictionary is omitted it defaults to the *globals* dictionary.
+ If both dictionaries are omitted, the expression is executed in the environment
+ where :func:`execfile` is called. The return value is ``None``.
+
+ .. warning::
+
+ The default *locals* act as described for function :func:`locals` below:
+ modifications to the default *locals* dictionary should not be attempted. Pass
+ an explicit *locals* dictionary if you need to see effects of the code on
+ *locals* after function :func:`execfile` returns. :func:`execfile` cannot be
+ used reliably to modify a function's locals.
+
+
+.. function:: file(filename[, mode[, bufsize]])
+
+ Constructor function for the :class:`file` type, described further in section
+ :ref:`bltin-file-objects`. The constructor's arguments are the same as those
+ of the :func:`open` built-in function described below.
+
+ When opening a file, it's preferable to use :func:`open` instead of invoking
+ this constructor directly. :class:`file` is more suited to type testing (for
+ example, writing ``isinstance(f, file)``).
+
+ .. versionadded:: 2.2
+
+
+.. function:: filter(function, iterable)
+
+ Construct a list from those elements of *iterable* for which *function* returns
+ true. *iterable* may be either a sequence, a container which supports
+ iteration, or an iterator, If *iterable* is a string or a tuple, the result
+ also has that type; otherwise it is always a list. 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 ``[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``.
+
+
+.. function:: float([x])
+
+ Convert a string or a number to floating point. If the argument is a string, it
+ must contain a possibly signed decimal or floating point number, possibly
+ embedded in whitespace. Otherwise, the argument may be a plain or long integer
+ or a floating point number, and a floating point number with the same value
+ (within Python's floating point precision) is returned. If no argument is
+ given, returns ``0.0``.
+
+ .. note::
+
+ .. index::
+ single: NaN
+ single: Infinity
+
+ When passing in a string, values for NaN and Infinity may be returned, depending
+ on the underlying C library. The specific set of strings accepted which cause
+ these values to be returned depends entirely on the C library and is known to
+ vary.
+
+ The float type is described in :ref:`typesnumeric`.
+
+.. function:: frozenset([iterable])
+ :noindex:
+
+ Return a frozenset object, optionally with elements taken from *iterable*.
+ The frozenset type is described in :ref:`types-set`.
+
+ For other containers see the built in :class:`dict`, :class:`list`, and
+ :class:`tuple` classes, and the :mod:`collections` module.
+
+ .. versionadded:: 2.4
+
+
+.. function:: getattr(object, name[, default])
+
+ Return the value of the named attributed 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
+ exception 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).
+
+
+.. 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.
+
+ .. versionadded:: 2.2
+
+
+.. function:: hex(x)
+
+ Convert an integer number (of any size) to a hexadecimal string. The result is a
+ valid Python expression.
+
+ .. versionchanged:: 2.4
+ Formerly only returned an unsigned literal.
+
+
+.. function:: id(object)
+
+ Return the "identity" of an object. This is an integer (or long 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.
+ (Implementation note: this is the address of the object.)
+
+
+.. function:: input([prompt])
+
+ Equivalent to ``eval(raw_input(prompt))``.
+
+ .. warning::
+
+ This function is not safe from user errors! It expects a valid Python
+ expression as input; if the input is not syntactically valid, a
+ :exc:`SyntaxError` will be raised. Other exceptions may be raised if there is an
+ error during evaluation. (On the other hand, sometimes this is exactly what you
+ need when writing a quick script for expert use.)
+
+ If the :mod:`readline` module was loaded, then :func:`input` will use it to
+ provide elaborate line editing and history features.
+
+ Consider using the :func:`raw_input` function for general input from users.
+
+
+.. function:: int([x[, radix]])
+
+ Convert a string or number to a plain integer. If the argument is a string, it
+ must contain a possibly signed decimal number representable as a Python integer,
+ possibly embedded in whitespace. The *radix* parameter gives the base for the
+ conversion and may be any integer in the range [2, 36], or zero. If *radix* is
+ zero, the proper radix is guessed based on the contents of string; the
+ interpretation is the same as for integer literals. If *radix* is specified and
+ *x* is not a string, :exc:`TypeError` is raised. Otherwise, the argument may be
+ a plain or long integer or a floating point number. Conversion of floating
+ point numbers to integers truncates (towards zero). If the argument is outside
+ the integer range a long object will be returned instead. If no arguments are
+ given, returns ``0``.
+
+ The integer type is described in :ref:`typesnumeric`.
+
+
+.. function:: isinstance(object, classinfo)
+
+ Return true if the *object* argument is an instance of the *classinfo* argument,
+ or of a (direct or indirect) subclass thereof. Also return true if *classinfo*
+ is a type object (new-style class) and *object* is an object of that type or of
+ a (direct or indirect) subclass thereof. If *object* is not a class instance or
+ an object of the given type, the function always returns false. If *classinfo*
+ is neither a class object nor a type object, it may be a tuple of class or type
+ objects, or may recursively contain other such tuples (other sequence types are
+ not accepted). If *classinfo* is not a class, type, or tuple of classes, types,
+ and such tuples, a :exc:`TypeError` exception is raised.
+
+ .. versionchanged:: 2.2
+ Support for a tuple of type information was added.
+
+
+.. function:: issubclass(class, classinfo)
+
+ Return true if *class* is a subclass (direct or indirect) 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.
+
+ .. versionchanged:: 2.3
+ Support for a tuple of type information was added.
+
+
+.. function:: iter(o[, sentinel])
+
+ Return an iterator object. The first argument is interpreted very differently
+ depending on the presence of the second argument. Without a second argument, *o*
+ 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 *o* must be a callable object. The
+ iterator created in this case will call *o* with no arguments for each call to
+ its :meth:`next` method; if the value returned is equal to *sentinel*,
+ :exc:`StopIteration` will be raised, otherwise the value will be returned.
+
+ .. versionadded:: 2.2
+
+
+.. 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).
+
+
+.. function:: list([iterable])
+
+ 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`. For other containers see the built in :class:`dict`,
+ :class:`set`, and :class:`tuple` classes, and the :mod:`collections` module.
+
+
+.. function:: locals()
+
+ Update and return a dictionary representing the current local symbol table.
+
+ .. warning::
+
+ The contents of this dictionary should not be modified; changes may not affect
+ the values of local variables used by the interpreter.
+
+ Free variables are returned by *locals* when it is called in a function block.
+ Modifications of free variables may not affect the values used by the
+ interpreter. Free variables are not returned in class blocks.
+
+
+.. function:: long([x[, radix]])
+
+ Convert a string or number to a long integer. If the argument is a string, it
+ must contain a possibly signed number of arbitrary size, possibly embedded in
+ whitespace. The *radix* argument is interpreted in the same way as for
+ :func:`int`, and may only be given when *x* is a string. Otherwise, the argument
+ may be a plain or long integer or a floating point number, and a long integer
+ with the same value is returned. Conversion of floating point numbers to
+ integers truncates (towards zero). If no arguments are given, returns ``0L``.
+
+ The long type is described in :ref:`typesnumeric`.
+
+.. function:: map(function, iterable, ...)
+
+ Apply *function* to every item of *iterable* and return a list of 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. If one
+ iterable is shorter than another it is assumed to be extended with ``None``
+ items. If *function* is ``None``, the identity function is assumed; if there
+ are multiple arguments, :func:`map` returns a list consisting of tuples
+ containing the corresponding items from all iterables (a kind of transpose
+ operation). The *iterable* arguments may be a sequence or any iterable object;
+ the result is always a list.
+
+
+.. function:: max(iterable[, args...][key])
+
+ With a single argument *iterable*, return the largest item of a non-empty
+ iterable (such as a string, tuple or list). With more than one argument, return
+ the largest of the arguments.
+
+ The optional *key* argument specifies a one-argument ordering function like that
+ used for :meth:`list.sort`. The *key* argument, if supplied, must be in keyword
+ form (for example, ``max(a,b,c,key=func)``).
+
+ .. versionchanged:: 2.5
+ Added support for the optional *key* argument.
+
+
+.. function:: min(iterable[, args...][key])
+
+ With a single argument *iterable*, return the smallest item of a non-empty
+ iterable (such as a string, tuple or list). With more than one argument, return
+ the smallest of the arguments.
+
+ The optional *key* argument specifies a one-argument ordering function like that
+ used for :meth:`list.sort`. The *key* argument, if supplied, must be in keyword
+ form (for example, ``min(a,b,c,key=func)``).
+
+ .. versionchanged:: 2.5
+ Added support for the optional *key* argument.
+
+
+.. function:: object()
+
+ Return a new featureless object. :class:`object` is a base for all new style
+ classes. It has the methods that are common to all instances of new style
+ classes.
+
+ .. versionadded:: 2.2
+
+ .. versionchanged:: 2.3
+ This function does not accept any arguments. Formerly, it accepted arguments but
+ ignored them.
+
+
+.. function:: oct(x)
+
+ Convert an integer number (of any size) to an octal string. The result is a
+ valid Python expression.
+
+ .. versionchanged:: 2.4
+ Formerly only returned an unsigned literal.
+
+
+.. function:: open(filename[, mode[, bufsize]])
+
+ Open a file, returning an object of the :class:`file` type described in
+ section :ref:`bltin-file-objects`. If the file cannot be opened,
+ :exc:`IOError` is raised. When opening a file, it's preferable to use
+ :func:`open` instead of invoking the :class:`file` constructor directly.
+
+ The first two arguments are the same as for ``stdio``'s :cfunc:`fopen`:
+ *filename* is the file name to be opened, and *mode* is a string indicating how
+ the file is to be opened.
+
+ The most commonly-used values of *mode* are ``'r'`` for reading, ``'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). If *mode* is omitted, it
+ defaults to ``'r'``. When opening a binary file, you should append ``'b'`` to
+ the *mode* value to open the file in binary mode, which will improve
+ portability. (Appending ``'b'`` is useful even on systems that don't treat
+ binary and text files differently, where it serves as documentation.) See below
+ for more possible values of *mode*.
+
+ .. index::
+ single: line-buffered I/O
+ single: unbuffered I/O
+ single: buffer size, I/O
+ single: I/O control; buffering
+
+ The optional *bufsize* argument specifies the file's desired buffer size: 0
+ means unbuffered, 1 means line buffered, any other positive value means use a
+ buffer of (approximately) that size. A negative *bufsize* means to use the
+ system default, which is usually line buffered for tty devices and fully
+ buffered for other files. If omitted, the system default is used. [#]_
+
+ Modes ``'r+'``, ``'w+'`` and ``'a+'`` open the file for updating (note that
+ ``'w+'`` truncates the file). Append ``'b'`` to the mode to open the file in
+ binary mode, on systems that differentiate between binary and text files; on
+ systems that don't have this distinction, adding the ``'b'`` has no effect.
+
+ In addition to the standard :cfunc:`fopen` values *mode* may be ``'U'`` or
+ ``'rU'``. Python is usually built with universal newline support; supplying
+ ``'U'`` opens the file as a text file, but lines may be terminated by any of the
+ following: the Unix end-of-line convention ``'\n'``, the Macintosh convention
+ ``'\r'``, or the Windows convention ``'\r\n'``. All of these external
+ representations are seen as ``'\n'`` by the Python program. If Python is built
+ without universal newline support a *mode* with ``'U'`` is the same as normal
+ text mode. Note that file objects so opened also have an attribute called
+ :attr:`newlines` which has a value of ``None`` (if no newlines have yet been
+ seen), ``'\n'``, ``'\r'``, ``'\r\n'``, or a tuple containing all the newline
+ types seen.
+
+ Python enforces that the mode, after stripping ``'U'``, begins with ``'r'``,
+ ``'w'`` or ``'a'``.
+
+ See also the :mod:`fileinput` module.
+
+ .. versionchanged:: 2.5
+ Restriction on first letter of mode string introduced.
+
+
+.. function:: ord(c)
+
+ Given a string of length one, return an integer representing the Unicode code
+ point of the character when the argument is a unicode object, or the value of
+ the byte when the argument is an 8-bit string. For example, ``ord('a')`` returns
+ the integer ``97``, ``ord(u'\u2020')`` returns ``8224``. This is the inverse of
+ :func:`chr` for 8-bit strings and of :func:`unichr` for unicode objects. If a
+ unicode argument is given and Python was built with UCS2 Unicode, then the
+ character's code point must be in the range [0..65535] inclusive; otherwise the
+ string length is two, and a :exc:`TypeError` will be raised.
+
+
+.. 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 int and long 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``. (This last feature was added in Python 2.2. In
+ Python 2.1 and before, if both arguments were of integer types and the second
+ argument was negative, an exception was raised.) 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. (This restriction was
+ added in Python 2.2. In Python 2.1 and before, floating 3-argument ``pow()``
+ returned platform-dependent results depending on floating-point rounding
+ accidents.)
+
+
+.. function:: property([fget[, fset[, fdel[, doc]]]])
+
+ Return a property attribute for new-style classes (classes that derive from
+ :class:`object`).
+
+ *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(object):
+ 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 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 decorator::
+
+ class Parrot(object):
+ 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.
+
+ .. versionadded:: 2.2
+
+ .. versionchanged:: 2.5
+ Use *fget*'s docstring if no *doc* given.
+
+
+.. function:: range([start,] stop[, step])
+
+ This is a versatile function to create lists containing arithmetic progressions.
+ It is most often used in :keyword:`for` loops. The arguments must be plain
+ 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 a list
+ of plain 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::
+
+ >>> range(10)
+ [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+ >>> range(1, 11)
+ [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+ >>> range(0, 30, 5)
+ [0, 5, 10, 15, 20, 25]
+ >>> range(0, 10, 3)
+ [0, 3, 6, 9]
+ >>> range(0, -10, -1)
+ [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
+ >>> range(0)
+ []
+ >>> range(1, 0)
+ []
+
+
+.. function:: raw_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 = raw_input('--> ')
+ --> Monty Python's Flying Circus
+ >>> s
+ "Monty Python's Flying Circus"
+
+ If the :mod:`readline` module was loaded, then :func:`raw_input` will use it to
+ provide elaborate line editing and history features.
+
+
+.. function:: reduce(function, iterable[, initializer])
+
+ Apply *function* of two arguments cumulatively to the items of *iterable*, from
+ left to right, so as to reduce the iterable to a single value. For example,
+ ``reduce(lambda x, y: x+y, [1, 2, 3, 4, 5])`` calculates ``((((1+2)+3)+4)+5)``.
+ The left argument, *x*, is the accumulated value and the right argument, *y*, is
+ the update value from the *iterable*. If the optional *initializer* is present,
+ it is placed before the items of the iterable in the calculation, and serves as
+ a default when the iterable is empty. If *initializer* is not given and
+ *iterable* contains only one item, the first item is returned.
+
+
+.. function:: reload(module)
+
+ Reload a previously imported *module*. The argument must be a module object, so
+ it must have been successfully imported before. This is useful if you have
+ edited the module source file using an external editor and want to try out the
+ new version without leaving the Python interpreter. The return value is the
+ module object (the same as the *module* argument).
+
+ When ``reload(module)`` is executed:
+
+ * Python modules' code is recompiled and the module-level code reexecuted,
+ defining a new set of objects which are bound to names in the module's
+ dictionary. The ``init`` function of extension modules is not called a second
+ time.
+
+ * As with all other objects in Python the old objects are only reclaimed after
+ their reference counts drop to zero.
+
+ * The names in the module namespace are updated to point to any new or changed
+ objects.
+
+ * Other references to the old objects (such as names external to the module) are
+ not rebound to refer to the new objects and must be updated in each namespace
+ where they occur if that is desired.
+
+ There are a number of other caveats:
+
+ If a module is syntactically correct but its initialization fails, the first
+ :keyword:`import` statement for it does not bind its name locally, but does
+ store a (partially initialized) module object in ``sys.modules``. To reload the
+ module you must first :keyword:`import` it again (this will bind the name to the
+ partially initialized module object) before you can :func:`reload` it.
+
+ When a module is reloaded, its dictionary (containing the module's global
+ variables) is retained. Redefinitions of names will override the old
+ definitions, so this is generally not a problem. If the new version of a module
+ does not define a name that was defined by the old version, the old definition
+ remains. This feature can be used to the module's advantage if it maintains a
+ global table or cache of objects --- with a :keyword:`try` statement it can test
+ for the table's presence and skip its initialization if desired::
+
+ try:
+ cache
+ except NameError:
+ cache = {}
+
+ It is legal though generally not very useful to reload built-in or dynamically
+ loaded modules, except for :mod:`sys`, :mod:`__main__` and :mod:`__builtin__`.
+ In many cases, however, extension modules are not designed to be initialized
+ more than once, and may fail in arbitrary ways when reloaded.
+
+ If a module imports objects from another module using :keyword:`from` ...
+ :keyword:`import` ..., calling :func:`reload` for the other module does not
+ redefine the objects imported from it --- one way around this is to re-execute
+ the :keyword:`from` statement, another is to use :keyword:`import` and qualified
+ names (*module*.*name*) instead.
+
+ If a module instantiates instances of a class, reloading the module that defines
+ the class does not affect the method definitions of the instances --- they
+ continue to use the old class definition. The same is true for derived classes.
+
+
+.. function:: repr(object)
+
+ Return a string containing a printable representation of an object. This is the
+ same value yielded by conversions (reverse quotes). It is sometimes useful to be
+ able to access this operation as an ordinary function. 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`.
+
+
+.. function:: reversed(seq)
+
+ Return a reverse iterator. *seq* must be an object which supports the sequence
+ protocol (the :meth:`__len__` method and the :meth:`__getitem__` method with
+ integer arguments starting at ``0``).
+
+ .. versionadded:: 2.4
+
+
+.. function:: round(x[, n])
+
+ Return the floating point value *x* rounded to *n* digits after the decimal
+ point. If *n* is omitted, it defaults to zero. The result is a floating point
+ number. Values are rounded to the closest multiple of 10 to the power minus
+ *n*; if two multiples are equally close, rounding is done away from 0 (so. for
+ example, ``round(0.5)`` is ``1.0`` and ``round(-0.5)`` is ``-1.0``).
+
+
+.. function:: set([iterable])
+ :noindex:
+
+ Return a new set, optionally with elements are taken from *iterable*.
+ The set type is described in :ref:`types-set`.
+
+ For other containers see the built in :class:`dict`, :class:`list`, and
+ :class:`tuple` classes, and the :mod:`collections` module.
+
+ .. versionadded:: 2.4
+
+
+.. 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([start,] stop[, step])
+
+ .. index:: single: Numerical Python
+
+ Return a 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:`start`,
+ :attr:`stop` and :attr:`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]``.
+
+
+.. function:: sorted(iterable[, cmp[, key[, reverse]]])
+
+ Return a new sorted list from the items in *iterable*.
+
+ The optional arguments *cmp*, *key*, and *reverse* have the same meaning as
+ those for the :meth:`list.sort` method (described in section
+ :ref:`typesseq-mutable`).
+
+ *cmp* specifies a custom comparison function of two arguments (iterable
+ elements) which should return a negative, zero or positive number depending on
+ whether the first argument is considered smaller than, equal to, or larger than
+ the second argument: ``cmp=lambda x,y: cmp(x.lower(), y.lower())``
+
+ *key* specifies a function of one argument that is used to extract a comparison
+ key from each list element: ``key=str.lower``
+
+ *reverse* is a boolean value. If set to ``True``, then the list elements are
+ sorted as if each comparison were reversed.
+
+ In general, the *key* and *reverse* conversion processes are much faster than
+ specifying an equivalent *cmp* function. This is because *cmp* is called
+ multiple times for each list element while *key* and *reverse* touch each
+ element only once.
+
+ .. versionadded:: 2.4
+
+
+.. 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 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++. For a more
+ advanced concept, see :func:`classmethod` in this section.
+
+ For more information on static methods, consult the documentation on the
+ standard type hierarchy in :ref:`types`.
+
+ .. versionadded:: 2.2
+
+ .. versionchanged:: 2.4
+ Function decorator syntax added.
+
+
+.. function:: str([object])
+
+ Return a string containing a nicely printable representation of an object. For
+ strings, this returns the string itself. The difference with ``repr(object)``
+ is that ``str(object)`` does not always attempt to return a string that is
+ acceptable to :func:`eval`; its goal is to return a printable string. If no
+ argument is given, returns the empty string, ``''``.
+
+ For more information on strings see :ref:`typesseq` which describes sequence
+ functionality (strings are sequences), and also the string-specific methods
+ described in the :ref:`string-methods` section. To output formatted strings
+ use template strings or the ``%`` operator described in the
+ :ref:`string-formatting` section. In addition see the :ref:`stringservices`
+ section. See also :func:`unicode`.
+
+
+.. 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 are not allowed to be strings. The fast, correct way to concatenate a
+ sequence of strings is by calling ``''.join(sequence)``. Note that
+ ``sum(range(n), m)`` is equivalent to ``reduce(operator.add, range(n), m)``
+
+ .. versionadded:: 2.3
+
+
+.. function:: super(type[, object-or-type])
+
+ Return the superclass of *type*. 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. :func:`super` only works for new-style
+ classes.
+
+ A typical use for calling a cooperative superclass method is::
+
+ class C(B):
+ def meth(self, arg):
+ super(C, self).meth(arg)
+
+ Note that :func:`super` is implemented as part of the binding process for
+ explicit dotted attribute lookups such as ``super(C, self).__getitem__(name)``.
+ Accordingly, :func:`super` is undefined for implicit lookups using statements or
+ operators such as ``super(C, self)[name]``.
+
+ .. versionadded:: 2.2
+
+
+.. function:: tuple([iterable])
+
+ 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`. For other containers see the built in :class:`dict`,
+ :class:`list`, and :class:`set` classes, and the :mod:`collections` module.
+
+
+.. function:: type(object)
+
+ .. index:: object: type
+
+ Return the type of an *object*. The return value is a type object. The
+ :func:`isinstance` built-in function is recommended for testing the type of an
+ object.
+
+ With three arguments, :func:`type` functions as a constructor as detailed below.
+
+
+.. function:: type(name, bases, dict)
+ :noindex:
+
+ 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:`__name__` attribute; the *bases* tuple itemizes the base classes and
+ becomes the :attr:`__bases__` attribute; and the *dict* dictionary is the
+ namespace containing definitions for class body and becomes the :attr:`__dict__`
+ attribute. For example, the following two statements create identical
+ :class:`type` objects::
+
+ >>> class X(object):
+ ... a = 1
+ ...
+ >>> X = type('X', (object,), dict(a=1))
+
+ .. versionadded:: 2.2
+
+
+.. function:: unichr(i)
+
+ Return the Unicode string of one character whose Unicode code is the integer
+ *i*. For example, ``unichr(97)`` returns the string ``u'a'``. This is the
+ inverse of :func:`ord` for Unicode strings. The valid range for the argument
+ depends how Python was configured -- it may be either UCS2 [0..0xFFFF] or UCS4
+ [0..0x10FFFF]. :exc:`ValueError` is raised otherwise. For ASCII and 8-bit
+ strings see :func:`chr`.
+
+ .. versionadded:: 2.0
+
+
+.. function:: unicode([object[, encoding [, errors]]])
+
+ Return the Unicode string version of *object* using one of the following modes:
+
+ If *encoding* and/or *errors* are given, ``unicode()`` will decode the object
+ which can either be an 8-bit string or a character buffer using the codec for
+ *encoding*. The *encoding* parameter is a string giving the name of an encoding;
+ if the encoding is not known, :exc:`LookupError` is raised. Error handling is
+ done according to *errors*; this specifies the treatment of characters which are
+ invalid in the input encoding. If *errors* is ``'strict'`` (the default), a
+ :exc:`ValueError` is raised on errors, while a value of ``'ignore'`` causes
+ errors to be silently ignored, and a value of ``'replace'`` causes the official
+ Unicode replacement character, ``U+FFFD``, to be used to replace input
+ characters which cannot be decoded. See also the :mod:`codecs` module.
+
+ If no optional parameters are given, ``unicode()`` will mimic the behaviour of
+ ``str()`` except that it returns Unicode strings instead of 8-bit strings. More
+ precisely, if *object* is a Unicode string or subclass it will return that
+ Unicode string without any additional decoding applied.
+
+ For objects which provide a :meth:`__unicode__` method, it will call this method
+ without arguments to create a Unicode string. For all other objects, the 8-bit
+ string version or representation is requested and then converted to a Unicode
+ string using the codec for the default encoding in ``'strict'`` mode.
+
+ For more information on Unicode strings see :ref:`typesseq` which describes
+ sequence functionality (Unicode strings are sequences), and also the
+ string-specific methods described in the :ref:`string-methods` section. To
+ output formatted strings use template strings or the ``%`` operator described
+ in the :ref:`string-formatting` section. In addition see the
+ :ref:`stringservices` section. See also :func:`str`.
+
+ .. versionadded:: 2.0
+
+ .. versionchanged:: 2.2
+ Support for :meth:`__unicode__` added.
+
+
+.. function:: vars([object])
+
+ Without arguments, return a dictionary corresponding to the current local symbol
+ table. With a module, class or class instance object as argument (or anything
+ else that has a :attr:`__dict__` attribute), returns a dictionary corresponding
+ to the object's symbol table. The returned dictionary should not be modified:
+ the effects on the corresponding symbol table are undefined. [#]_
+
+
+.. function:: xrange([start,] stop[, step])
+
+ This function is very similar to :func:`range`, but returns an "xrange object"
+ instead of a list. This is an opaque sequence type which yields the same values
+ as the corresponding list, without actually storing them all simultaneously.
+ The advantage of :func:`xrange` over :func:`range` is minimal (since
+ :func:`xrange` still has to create the values when asked for them) except when a
+ very large range is used on a memory-starved machine or when all of the range's
+ elements are never used (such as when the loop is usually terminated with
+ :keyword:`break`).
+
+ .. note::
+
+ :func:`xrange` is intended to be simple and fast. Implementations may impose
+ restrictions to achieve this. The C implementation of Python restricts all
+ arguments to native C longs ("short" Python integers), and also requires that
+ the number of elements fit in a native C long.
+
+
+.. function:: zip([iterable, ...])
+
+ This function returns a list of tuples, where the *i*-th tuple contains the
+ *i*-th element from each of the argument sequences or iterables. The returned
+ list is truncated in length to the length of the shortest argument sequence.
+ When there are multiple arguments which are all of the same length, :func:`zip`
+ is similar to :func:`map` with an initial argument of ``None``. With a single
+ sequence argument, it returns a list of 1-tuples. With no arguments, it returns
+ an empty list.
+
+ .. versionadded:: 2.0
+
+ .. versionchanged:: 2.4
+ Formerly, :func:`zip` required at least one argument and ``zip()`` raised a
+ :exc:`TypeError` instead of returning an empty list.
+
+.. % ---------------------------------------------------------------------------
+
+
+.. _non-essential-built-in-funcs:
+
+Non-essential Built-in Functions
+================================
+
+There are several built-in functions that are no longer essential to learn, know
+or use in modern Python programming. They have been kept here to maintain
+backwards compatibility with programs written for older versions of Python.
+
+Python programmers, trainers, students and bookwriters should feel free to
+bypass these functions without concerns about missing something important.
+
+
+.. function:: apply(function, args[, keywords])
+
+ The *function* argument must be a callable object (a user-defined or built-in
+ function or method, or a class object) and the *args* argument must be a
+ sequence. The *function* is called with *args* as the argument list; the number
+ of arguments is the length of the tuple. If the optional *keywords* argument is
+ present, it must be a dictionary whose keys are strings. It specifies keyword
+ arguments to be added to the end of the argument list. Calling :func:`apply` is
+ different from just calling ``function(args)``, since in that case there is
+ always exactly one argument. The use of :func:`apply` is equivalent to
+ ``function(*args, **keywords)``. Use of :func:`apply` is not necessary since the
+ "extended call syntax," as used in the last example, is completely equivalent.
+
+ .. deprecated:: 2.3
+ Use the extended call syntax instead, as described above.
+
+
+.. function:: buffer(object[, offset[, size]])
+
+ The *object* argument must be an object that supports the buffer call interface
+ (such as strings, arrays, and buffers). A new buffer object will be created
+ which references the *object* argument. The buffer object will be a slice from
+ the beginning of *object* (or from the specified *offset*). The slice will
+ extend to the end of *object* (or will have a length given by the *size*
+ argument).
+
+
+.. function:: coerce(x, y)
+
+ Return a tuple consisting of the two numeric arguments converted to a common
+ type, using the same rules as used by arithmetic operations. If coercion is not
+ possible, raise :exc:`TypeError`.
+
+
+.. function:: intern(string)
+
+ Enter *string* in the table of "interned" strings and return the interned string
+ -- which is *string* itself or a copy. Interning strings is useful to gain a
+ little performance on dictionary lookup -- if the keys in a dictionary are
+ interned, and the lookup key is interned, the key comparisons (after hashing)
+ can be done by a pointer compare instead of a string compare. Normally, the
+ names used in Python programs are automatically interned, and the dictionaries
+ used to hold module, class or instance attributes have interned keys.
+
+ .. versionchanged:: 2.3
+ Interned strings are not immortal (like they used to be in Python 2.2 and
+ before); you must keep a reference to the return value of :func:`intern` around
+ to benefit from it.
+
+.. rubric:: Footnotes
+
+.. [#] It is used relatively rarely so does not warrant being made into a statement.
+
+.. [#] Specifying a buffer size currently has no effect on systems that don't have
+ :cfunc:`setvbuf`. The interface to specify the buffer size is not done using a
+ method that calls :cfunc:`setvbuf`, because that may dump core when called after
+ any I/O has been performed, and there's no reliable way to determine whether
+ this is the case.
+
+.. [#] In the current implementation, local variable bindings cannot normally be
+ affected this way, but variables retrieved from other scopes (such as modules)
+ can be. This may change.
+