
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.

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.

all(iterable)

   Return True if all elements of the *iterable* are true (or if the
   iterable is empty).  Equivalent to:

      def all(iterable):
          for element in iterable:
              if not element:
                  return False
          return True

   New in version 2.5.

any(iterable)

   Return True if any element of the *iterable* is true.  If the
   iterable is empty, return False.  Equivalent to:

      def any(iterable):
          for element in iterable:
              if element:
                  return True
          return False

   New in version 2.5.

basestring()

   This abstract type is the superclass for ``str`` and ``unicode``.
   It cannot be called or instantiated, but it can be used to test
   whether an object is an instance of ``str`` or ``unicode``.
   ``isinstance(obj, basestring)`` is equivalent to ``isinstance(obj,
   (str, unicode))``.

   New in version 2.3.

bin(x)

   Convert an integer number to a binary string. The result is a valid
   Python expression.  If *x* is not a Python ``int`` object, it has
   to define an ``__index__()`` method that returns an integer.

   New in version 2.6.

bool([x])

   Convert a value to a Boolean, using the standard truth testing
   procedure.  If *x* is false or omitted, this returns ``False``;
   otherwise it returns ``True``. ``bool`` is also a class, which is a
   subclass of ``int``. Class ``bool`` cannot be subclassed further.
   Its only instances are ``False`` and ``True``.

   New in version 2.2.1.

   Changed in version 2.3: If no argument is given, this function
   returns ``False``.

callable(object)

   Return ``True`` if the *object* argument appears callable,
   ``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
   ``__call__()`` method.

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 ``ord()``.  The argument must be in the range
   [0..255], inclusive; ``ValueError`` will be raised if *i* is
   outside that range. See also ``unichr()``.

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 *Function definitions* 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 ``staticmethod()`` in this section.

   For more information on class methods, consult the documentation on
   the standard type hierarchy in *The standard type hierarchy*.

   New in version 2.2.

   Changed in version 2.4: Function decorator syntax added.

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``.

compile(source, filename, mode[, flags[, dont_inherit]])

   Compile the *source* into a code or AST object.  Code objects can
   be executed by an ``exec`` statement or evaluated by a call to
   ``eval()``. *source* can either be a string or an AST object.
   Refer to the ``ast`` module documentation for information on how to
   work with AST objects.

   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
   other than ``None`` will be printed).

   The optional arguments *flags* and *dont_inherit* 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 ORed
   together to specify multiple statements.  The bitfield required to
   specify a given feature can be found as the ``compiler_flag``
   attribute on the ``_Feature`` instance in the ``__future__``
   module.

   This function raises ``SyntaxError`` if the compiled source is
   invalid, and ``TypeError`` if the source contains null bytes.

   Note: When compiling a string with multi-line code, 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 ``str.replace()``
     to change them into ``'\n'``.

   Changed in version 2.3: The *flags* and *dont_inherit* arguments
   were added.

   Changed in version 2.6: Support for compiling AST objects.

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
   ``int()``, ``long()`` and ``float()``.  If both arguments are
   omitted, returns ``0j``.

   The complex type is described in *Numeric Types --- int, float,
   long, complex*.

delattr(object, name)

   This is a relative of ``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``.

dict([arg])

   Create a new data dictionary, optionally with items taken from
   *arg*. The dictionary type is described in *Mapping Types ---
   dict*.

   For other containers see the built in ``list``, ``set``, and
   ``tuple`` classes, and the ``collections`` module.

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 ``__dir__()``, this method will be
   called and must return the list of attributes. This allows objects
   that implement a custom ``__getattr__()`` or ``__getattribute__()``
   function to customize the way ``dir()`` reports their attributes.

   If the object does not provide ``__dir__()``, the function tries
   its best to gather information from the object's ``__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 ``__getattr__()``.

   The default ``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()   # doctest: +SKIP
   ['__builtins__', '__doc__', '__name__', 'struct']
   >>> dir(struct)   # doctest: +NORMALIZE_WHITESPACE
   ['Struct', '__builtins__', '__doc__', '__file__', '__name__',
    '__package__', '_clearcache', 'calcsize', 'error', 'pack', 'pack_into',
    'unpack', 'unpack_from']
   >>> class Foo(object):
   ...     def __dir__(self):
   ...         return ["kan", "ga", "roo"]
   ...
   >>> f = Foo()
   >>> dir(f)
   ['ga', 'kan', 'roo']

   Note: Because ``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.  For example, metaclass attributes are
     not in the result list when the argument is a class.

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)``.

   Changed in version 2.3: Using ``divmod()`` with complex numbers is
   deprecated.

enumerate(sequence[, start=0])

   Return an enumerate object. *sequence* must be a sequence, an
   *iterator*, or some other object which supports iteration.  The
   ``next()`` method of the iterator returned by ``enumerate()``
   returns a tuple containing a count (from *start* which defaults to
   0) and the corresponding value obtained from iterating over
   *iterable*. ``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

   New in version 2.3.

   New in version 2.6: The *start* parameter.

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.

   Changed in version 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 namespace.
   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 ``__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 ``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 ``compile()``).  In this case pass a code
   object instead of a string.  If the code object has been compiled
   with ``'exec'`` as the *mode* argument, ``eval()``'s return value
   will be ``None``.

   Hints: dynamic execution of statements is supported by the ``exec``
   statement.  Execution of statements from a file is supported by the
   ``execfile()`` function.  The ``globals()`` and ``locals()``
   functions returns the current global and local dictionary,
   respectively, which may be useful to pass around for use by
   ``eval()`` or ``execfile()``.

execfile(filename[, globals[, locals]])

   This function is similar to the ``exec`` statement, but parses a
   file instead of a string.  It is different from the ``import``
   statement in that it does not use the module administration --- it
   reads the file unconditionally and does not create a new module.
   [1]

   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.

   Changed in version 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 ``execfile()`` is called.  The
   return value is ``None``.

   Note: The default *locals* act as described for function ``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
     ``execfile()`` returns.  ``execfile()`` cannot be used reliably
     to modify a function's locals.

file(filename[, mode[, bufsize]])

   Constructor function for the ``file`` type, described further in
   section *File Objects*.  The constructor's arguments are the same
   as those of the ``open()`` built-in function described below.

   When opening a file, it's preferable to use ``open()`` instead of
   invoking this constructor directly.  ``file`` is more suited to
   type testing (for example, writing ``isinstance(f, file)``).

   New in version 2.2.

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``.

   See ``itertools.ifilter()`` and ``itertools.ifilterfalse()`` for
   iterator versions of this function, including a variation that
   filters for elements where the *function* returns false.

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. The argument may
   also be [+|-]nan or [+|-]inf. 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: When passing in a string, values for NaN and Infinity may be
     returned, depending on the underlying C library.  Float accepts
     the strings nan, inf and -inf for NaN and positive or negative
     infinity. The case and a leading + are ignored as well as a
     leading - is ignored for NaN. Float always represents NaN and
     infinity as nan, inf or -inf.

   The float type is described in *Numeric Types --- int, float, long,
   complex*.

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: *Format
   Specification Mini-Language*.

   Note: ``format(value, format_spec)`` merely calls
     ``value.__format__(format_spec)``.

   New in version 2.6.

frozenset([iterable])

   Return a frozenset object, optionally with elements taken from
   *iterable*. The frozenset type is described in *Set Types --- set,
   frozenset*.

   For other containers see the built in ``dict``, ``list``, and
   ``tuple`` classes, and the ``collections`` module.

   New in version 2.4.

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 ``AttributeError`` is raised.

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).

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.)

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).

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 ``site``
   module.

   New in version 2.2.

hex(x)

   Convert an integer number (of any size) to a hexadecimal string.
   The result is a valid Python expression.

   Note: To obtain a hexadecimal string representation for a float, use
     the ``float.hex()`` method.

   Changed in version 2.4: Formerly only returned an unsigned literal.

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 ``id()`` value.

   **CPython implementation detail:** This is the address of the
   object.

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 ``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 ``readline`` module was loaded, then ``input()`` will use it
   to provide elaborate line editing and history features.

   Consider using the ``raw_input()`` function for general input from
   users.

int([x[, base]])

   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 *base* parameter gives the base for the conversion (which is 10
   by default) and may be any integer in the range [2, 36], or zero.
   If *base* is zero, the proper radix is determined based on the
   contents of string; the interpretation is the same as for integer
   literals.  (See *Numeric literals*.)  If *base* is specified and
   *x* is not a string, ``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 *Numeric Types --- int, float,
   long, complex*.

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 ``TypeError`` exception is raised.

   Changed in version 2.2: Support for a tuple of type information was
   added.

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
   ``TypeError`` exception is raised.

   Changed in version 2.3: Support for a tuple of type information was
   added.

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 ``__iter__()`` method), or it
   must support the sequence protocol (the ``__getitem__()`` method
   with integer arguments starting at ``0``).  If it does not support
   either of those protocols, ``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 ``next()`` method; if the value returned is
   equal to *sentinel*, ``StopIteration`` will be raised, otherwise
   the value will be returned.

   One useful application of the second form of ``iter()`` is to read
   lines of a file until a certain line is reached.  The following
   example reads a file until ``"STOP"`` is reached:

      with open("mydata.txt") as fp:
          for line in iter(fp.readline, "STOP"):
              process_line(line)

   New in version 2.2.

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).

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, ``[]``.

   ``list`` is a mutable sequence type, as documented in *Sequence
   Types --- str, unicode, list, tuple, buffer, xrange*. For other
   containers see the built in ``dict``, ``set``, and ``tuple``
   classes, and the ``collections`` module.

locals()

   Update and return a dictionary representing the current local
   symbol table. Free variables are returned by ``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.

long([x[, base]])

   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 *base* argument is interpreted
   in the same way as for ``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 *Numeric Types --- int, float, long,
   complex*.

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, ``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.

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 ``list.sort()``.  The *key* argument,
   if supplied, must be in keyword form (for example,
   ``max(a,b,c,key=func)``).

   Changed in version 2.5: Added support for the optional *key*
   argument.

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 ``list.sort()``.  The *key* argument,
   if supplied, must be in keyword form (for example,
   ``min(a,b,c,key=func)``).

   Changed in version 2.5: Added support for the optional *key*
   argument.

next(iterator[, default])

   Retrieve the next item from the *iterator* by calling its
   ``next()`` method.  If *default* is given, it is returned if the
   iterator is exhausted, otherwise ``StopIteration`` is raised.

   New in version 2.6.

object()

   Return a new featureless object.  ``object`` is a base for all new
   style classes.  It has the methods that are common to all instances
   of new style classes.

   New in version 2.2.

   Changed in version 2.3: This function does not accept any
   arguments. Formerly, it accepted arguments but ignored them.

oct(x)

   Convert an integer number (of any size) to an octal string.  The
   result is a valid Python expression.

   Changed in version 2.4: Formerly only returned an unsigned literal.

open(filename[, mode[, bufsize]])

   Open a file, returning an object of the ``file`` type described in
   section *File Objects*.  If the file cannot be opened, ``IOError``
   is raised.  When opening a file, it's preferable to use ``open()``
   instead of invoking the ``file`` constructor directly.

   The first two arguments are the same as for ``stdio``'s
   ``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'``.  The default is to use text mode, which may convert
   ``'\n'`` characters to a platform-specific representation on
   writing and back on reading.  Thus, 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*.

   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. [2]

   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 ``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 ``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'``.

   Python provides many file handling modules including ``fileinput``,
   ``os``, ``os.path``, ``tempfile``, and ``shutil``.

   Changed in version 2.5: Restriction on first letter of mode string
   introduced.

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
   ``chr()`` for 8-bit strings and of ``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
   ``TypeError`` will be raised.

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.)

print([object, ...][, sep=' '][, end='\n'][, file=sys.stdout])

   Print *object*(s) 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 ``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 *object* is
   given, ``print()`` will just write *end*.

   The *file* argument must be an object with a ``write(string)``
   method; if it is not present or ``None``, ``sys.stdout`` will be
   used.

   Note: This function is not normally available as a built-in since the
     name ``print`` is recognized as the ``print`` statement.  To
     disable the statement and use the ``print()`` function, use this
     future statement at the top of your module:

        from __future__ import print_function

   New in version 2.6.

property([fget[, fset[, fdel[, doc]]]])

   Return a property attribute for *new-style class*es (classes that
   derive from ``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 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 ``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 ``voltage()`` method into a "getter" for a read-only
   attribute with the same name.

   A property object has ``getter``, ``setter``, and ``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(object):
          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.

   New in version 2.2.

   Changed in version 2.5: Use *fget*'s docstring if no *doc* given.

   Changed in version 2.6: The ``getter``, ``setter``, and ``deleter``
   attributes were added.

range([start], stop[, step])

   This is a versatile function to create lists containing arithmetic
   progressions. It is most often used in ``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 ``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)
   []

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, ``EOFError`` is raised.
   Example:

      >>> s = raw_input('--> ')
      --> Monty Python's Flying Circus
      >>> s
      "Monty Python's Flying Circus"

   If the ``readline`` module was loaded, then ``raw_input()`` will
   use it to provide elaborate line editing and history features.

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.

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 ``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 ``import`` it
   again (this will bind the name to the partially initialized module
   object) before you can ``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 ``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 ``sys``, ``__main__`` and
   ``__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 ``from`` ...
   ``import`` ..., calling ``reload()`` for the other module does not
   redefine the objects imported from it --- one way around this is to
   re-execute the ``from`` statement, another is to use ``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.

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 ``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 ``__repr__()``
   method.

reversed(seq)

   Return a reverse *iterator*.  *seq* must be an object which has a
   ``__reversed__()`` method or supports the sequence protocol (the
   ``__len__()`` method and the ``__getitem__()`` method with integer
   arguments starting at ``0``).

   New in version 2.4.

   Changed in version 2.6: Added the possibility to write a custom
   ``__reversed__()`` method.

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``).

set([iterable])

   Return a new set, optionally with elements taken from *iterable*.
   The set type is described in *Set Types --- set, frozenset*.

   For other containers see the built in ``dict``, ``list``, and
   ``tuple`` classes, and the ``collections`` module.

   New in version 2.4.

setattr(object, name, value)

   This is the counterpart of ``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``.

slice([start], stop[, step])

   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
   ``start``, ``stop`` and ``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
   ``itertools.islice()`` for an alternate version that returns an
   iterator.

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 ``list.sort()`` method (described in
   section *Mutable Sequence Types*).

   *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())``.  The
   default value is ``None``.

   *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.

   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.  To convert an
   old-style *cmp* function to a *key* function, see the CmpToKey
   recipe in the ASPN cookbook.

   For sorting examples and a brief sorting tutorial, see Sorting
   HowTo.

   New in version 2.4.

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 *Function definitions* 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 ``classmethod()`` in this section.

   For more information on static methods, consult the documentation
   on the standard type hierarchy in *The standard type hierarchy*.

   New in version 2.2.

   Changed in version 2.4: Function decorator syntax added.

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 ``eval()``;
   its goal is to return a printable string.  If no argument is given,
   returns the empty string, ``''``.

   For more information on strings see *Sequence Types --- str,
   unicode, list, tuple, buffer, xrange* which describes sequence
   functionality (strings are sequences), and also the string-specific
   methods described in the *String Methods* section. To output
   formatted strings use template strings or the ``%`` operator
   described in the *String Formatting Operations* section. In
   addition see the *String Services* section. See also ``unicode()``.

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)`` To add floating
   point values with extended precision, see ``math.fsum()``.

   New in version 2.3.

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 ``getattr()`` except that the *type* itself is
   skipped.

   The ``__mro__`` attribute of the *type* lists the method resolution
   search order used by both ``getattr()`` and ``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).

   Note: ``super()`` only works for *new-style class*es.

   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(C, self).method(arg)

   Note that ``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
   ``__getattribute__()`` method for searching classes in a
   predictable order that supports cooperative multiple inheritance.
   Accordingly, ``super()`` is undefined for implicit lookups using
   statements or operators such as ``super()[name]``.

   Also note that ``super()`` is not limited to use inside methods.
   The two argument form specifies the arguments exactly and makes the
   appropriate references.

   New in version 2.2.

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,
   ``()``.

   ``tuple`` is an immutable sequence type, as documented in *Sequence
   Types --- str, unicode, list, tuple, buffer, xrange*. For other
   containers see the built in ``dict``, ``list``, and ``set``
   classes, and the ``collections`` module.

type(object)

   Return the type of an *object*.  The return value is a type object.
   The ``isinstance()`` built-in function is recommended for testing
   the type of an object.

   With three arguments, ``type()`` functions as a constructor as
   detailed below.

type(name, bases, dict)

   Return a new type object.  This is essentially a dynamic form of
   the ``class`` statement. The *name* string is the class name and
   becomes the ``__name__`` attribute; the *bases* tuple itemizes the
   base classes and becomes the ``__bases__`` attribute; and the
   *dict* dictionary is the namespace containing definitions for class
   body and becomes the ``__dict__`` attribute.  For example, the
   following two statements create identical ``type`` objects:

   >>> class X(object):
   ...     a = 1
   ...
   >>> X = type('X', (object,), dict(a=1))

   New in version 2.2.

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 ``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].
   ``ValueError`` is raised otherwise. For ASCII and 8-bit strings see
   ``chr()``.

   New in version 2.0.

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, ``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 ``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 ``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 ``__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 *Sequence Types ---
   str, unicode, list, tuple, buffer, xrange* which describes sequence
   functionality (Unicode strings are sequences), and also the string-
   specific methods described in the *String Methods* section. To
   output formatted strings use template strings or the ``%`` operator
   described in the *String Formatting Operations* section. In
   addition see the *String Services* section. See also ``str()``.

   New in version 2.0.

   Changed in version 2.2: Support for ``__unicode__()`` added.

vars([object])

   Without an argument, act like ``locals()``.

   With a module, class or class instance object as argument (or
   anything else that has a ``__dict__`` attribute), return that
   attribute.

   Note: The returned dictionary should not be modified: the effects on
     the corresponding symbol table are undefined. [3]

xrange([start], stop[, step])

   This function is very similar to ``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
   ``xrange()`` over ``range()`` is minimal (since ``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 ``break``).

   **CPython implementation detail:** ``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.  If a
   larger range is needed, an alternate version can be crafted using
   the ``itertools`` module: ``takewhile(lambda x: x<stop,
   (start+i*step for i in count()))``.

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, ``zip()`` is similar to
   ``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.

   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)``.

   ``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)
      >>> zipped
      [(1, 4), (2, 5), (3, 6)]
      >>> x2, y2 = zip(*zipped)
      >>> x == list(x2) and y == list(y2)
      True

   New in version 2.0.

   Changed in version 2.4: Formerly, ``zip()`` required at least one
   argument and ``zip()`` raised a ``TypeError`` instead of returning
   an empty list.

__import__(name[, globals[, locals[, fromlist[, level]]]])

   Note: This is an advanced function that is not needed in everyday
     Python programming.

   This function is invoked by the ``import`` statement.  It can be
   replaced (by importing the ``__builtin__`` module and assigning to
   ``__builtin__.__import__``) in order to change semantics of the
   ``import`` statement, but nowadays it is usually simpler to use
   import hooks (see **PEP 302**).  Direct use of ``__import__()`` is
   rare, except in cases where you want to import a module whose name
   is only known at runtime.

   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 ``import`` statement.

   *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 ``__import__()``.

   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(), [], -1)

   The statement ``import spam.ham`` results in this call:

      spam = __import__('spam.ham', globals(), locals(), [], -1)

   Note how ``__import__()`` returns the toplevel module here because
   this is the object that is bound to a name by the ``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'], -1)
      eggs = _temp.eggs
      saus = _temp.sausage

   Here, the ``spam.ham`` module is returned from ``__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, you can call ``__import__()`` and then look it up
   in ``sys.modules``:

      >>> import sys
      >>> name = 'foo.bar.baz'
      >>> __import__(name)
      <module 'foo' from ...>
      >>> baz = sys.modules[name]
      >>> baz
      <module 'foo.bar.baz' from ...>

   Changed in version 2.5: The level parameter was added.

   Changed in version 2.5: Keyword support for parameters was added.


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 book writers should feel
free to bypass these functions without concerns about missing
something important.

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 ``apply()`` is
   different from just calling ``function(args)``, since in that case
   there is always exactly one argument.  The use of ``apply()`` is
   equivalent to ``function(*args, **keywords)``.

   Deprecated since version 2.3: Use the extended call syntax with
   ``*args`` and ``**keywords`` instead.

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).

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 ``TypeError``.

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.

   Changed in version 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 ``intern()`` around to benefit
   from it.

-[ Footnotes ]-

[1] It is used relatively rarely so does not warrant being made into a
    statement.

[2] Specifying a buffer size currently has no effect on systems that
    don't have ``setvbuf()``.  The interface to specify the buffer
    size is not done using a method that calls ``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.

[3] 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.
