1236 lines
52 KiB
ReStructuredText
1236 lines
52 KiB
ReStructuredText
.. XXX document all delegations to __special__ methods
|
|
.. _built-in-funcs:
|
|
|
|
Built-in Functions
|
|
==================
|
|
|
|
The Python interpreter has a number of functions and types built into it that
|
|
are always available. They are listed here in alphabetical order.
|
|
|
|
|
|
.. function:: abs(x)
|
|
|
|
Return the absolute value of a number. The argument may be an
|
|
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
|
|
|
|
|
|
.. 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
|
|
|
|
|
|
.. function:: ascii(object)
|
|
|
|
As :func:`repr`, return a string containing a printable representation of an
|
|
object, but escape the non-ASCII characters in the string returned by
|
|
:func:`repr` using ``\x``, ``\u`` or ``\U`` escapes. This generates a string
|
|
similar to that returned by :func:`repr` in Python 2.
|
|
|
|
|
|
.. function:: bin(x)
|
|
|
|
Convert an integer number to a binary string. The result is a valid Python
|
|
expression. If *x* is not a Python :class:`int` object, it has to define an
|
|
:meth:`__index__` method that returns an integer.
|
|
|
|
|
|
.. 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
|
|
|
|
|
|
.. function:: bytearray([arg[, encoding[, errors]]])
|
|
|
|
Return a new array of bytes. The :class:`bytearray` type is a mutable
|
|
sequence of integers in the range 0 <= x < 256. It has most of the usual
|
|
methods of mutable sequences, described in :ref:`typesseq-mutable`, as well
|
|
as most methods that the :class:`str` type has, see :ref:`bytes-methods`.
|
|
|
|
The optional *arg* parameter can be used to initialize the array in a few
|
|
different ways:
|
|
|
|
* If it is a *string*, you must also give the *encoding* (and optionally,
|
|
*errors*) parameters; :func:`bytearray` then converts the string to
|
|
bytes using :meth:`str.encode`.
|
|
|
|
* If it is an *integer*, the array will have that size and will be
|
|
initialized with null bytes.
|
|
|
|
* If it is an object conforming to the *buffer* interface, a read-only buffer
|
|
of the object will be used to initialize the bytes array.
|
|
|
|
* If it is an *iterable*, it must be an iterable of integers in the range
|
|
``0 <= x < 256``, which are used as the initial contents of the array.
|
|
|
|
Without an argument, an array of size 0 is created.
|
|
|
|
|
|
.. function:: bytes([arg[, encoding[, errors]]])
|
|
|
|
Return a new "bytes" object, which is an immutable sequence of integers in
|
|
the range ``0 <= x < 256``. :class:`bytes` is an immutable version of
|
|
:class:`bytearray` -- it has the same non-mutating methods and the same
|
|
indexing and slicing behavior.
|
|
|
|
Accordingly, constructor arguments are interpreted as for :func:`buffer`.
|
|
|
|
Bytes objects can also be created with literals, see :ref:`strings`.
|
|
|
|
|
|
.. function:: chr(i)
|
|
|
|
Return the string of one character whose Unicode codepoint is the integer
|
|
*i*. For example, ``chr(97)`` returns the string ``'a'``. This is the
|
|
inverse of :func:`ord`. The valid range for the argument depends how Python
|
|
was configured -- it may be either UCS2 [0..0xFFFF] or UCS4 [0..0x10FFFF].
|
|
:exc:`ValueError` will be raised if *i* is outside that range.
|
|
|
|
|
|
.. 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 :term:`decorator` -- see the description
|
|
of function definitions in :ref:`function` for details.
|
|
|
|
It can be called either on the class (such as ``C.f()``) or on an instance (such
|
|
as ``C().f()``). The instance is ignored except for its class. 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`.
|
|
|
|
|
|
.. 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 or AST object. Code objects can be executed
|
|
by an :keyword:`exec` statement or evaluated by a call to :func:`eval`.
|
|
*source* can either be a string or an AST object. Refer to the :mod:`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 else 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 :attr:`compiler_flag` attribute on the :class:`_Feature`
|
|
instance in the :mod:`__future__` module.
|
|
|
|
This function raises :exc:`SyntaxError` if the compiled source is invalid,
|
|
and :exc:`TypeError` if the source contains null bytes.
|
|
|
|
.. note::
|
|
|
|
When compiling a string with multi-line statements, 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 :meth:`str.replace` to change them into
|
|
``'\n'``.
|
|
|
|
|
|
.. 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`
|
|
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() # 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 :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. For example, metaclass attributes
|
|
are not in the result list when the argument is a class.
|
|
|
|
|
|
.. 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 integer division. With mixed
|
|
operand types, the rules for binary arithmetic operators apply. For 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)``.
|
|
|
|
|
|
.. function:: enumerate(iterable[, start=0])
|
|
|
|
Return an enumerate object. *iterable* must be a sequence, an
|
|
:term:`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 *start* which defaults to 0) 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
|
|
|
|
|
|
.. 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.
|
|
|
|
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 :mod:`builtins` 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 :func:`eval` is called. The return value is the result of
|
|
the evaluated expression. Syntax errors are reported as exceptions. Example:
|
|
|
|
>>> x = 1
|
|
>>> 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. If the code object has been compiled with ``'exec'`` as the
|
|
*kind* argument, :func:`eval`\'s return value will be ``None``.
|
|
|
|
Hints: dynamic execution of statements is supported by the :func:`exec`
|
|
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:`exec`.
|
|
|
|
|
|
.. function:: exec(object[, globals[, locals]])
|
|
|
|
This function supports dynamic execution of Python code. *object* must be
|
|
either a string or a code object. If it is a string, the string is parsed as
|
|
a suite of Python statements which is then executed (unless a syntax error
|
|
occurs). If it is a code object, it is simply executed. In all cases, the
|
|
code that's executed is expected to be valid as file input (see the section
|
|
"File input" in the Reference Manual). Be aware that the :keyword:`return`
|
|
and :keyword:`yield` statements may not be used outside of function
|
|
definitions even within the context of code passed to the :func:`exec`
|
|
function. The return value is ``None``.
|
|
|
|
In all cases, if the optional parts are omitted, the code is executed in the
|
|
current scope. If only *globals* is provided, it must be a dictionary, which
|
|
will be used for both the global and the local variables. If *globals* and
|
|
*locals* are given, they are used for the global and local variables,
|
|
respectively. If provided, *locals* can be any mapping object.
|
|
|
|
If the *globals* dictionary does not contain a value for the key
|
|
``__builtins__``, a reference to the dictionary of the built-in module
|
|
:mod:`builtins` is inserted under that key. That way you can control what
|
|
builtins are available to the executed code by inserting your own
|
|
``__builtins__`` dictionary into *globals* before passing it to :func:`exec`.
|
|
|
|
.. note::
|
|
|
|
The built-in functions :func:`globals` and :func:`locals` return the current
|
|
global and local dictionary, respectively, which may be useful to pass around
|
|
for use as the second and third argument to :func:`exec`.
|
|
|
|
.. 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:`exec` returns.
|
|
|
|
|
|
.. function:: filter(function, iterable)
|
|
|
|
Construct an iterator 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 *function* is ``None``, the identity
|
|
function is assumed, that is, all elements of *iterable* that are false are
|
|
removed.
|
|
|
|
Note that ``filter(function, iterable)`` is equivalent to the generator
|
|
expression ``(item for item in iterable if function(item))`` if function is
|
|
not ``None`` and ``(item for item in iterable if item)`` if function is
|
|
``None``.
|
|
|
|
|
|
.. 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. The argument may also be ``'[+|-]nan'`` or
|
|
``'[+|-]inf'``. Otherwise, the argument may be an 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,
|
|
``0.0`` is returned.
|
|
|
|
.. 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. 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 :ref:`typesnumeric`.
|
|
|
|
.. function:: format(value[, format_spec])
|
|
|
|
.. index::
|
|
pair: str; format
|
|
single: __format__
|
|
|
|
Convert a string or a number to a "formatted" representation, as controlled
|
|
by *format_spec*. The interpretation of *format_spec* will depend on the
|
|
type of the *value* argument, however there is a standard formatting syntax
|
|
that is used by most built-in types: :ref:`formatspec`.
|
|
|
|
.. note::
|
|
|
|
``format(value, format_spec)`` merely calls ``value.__format__(format_spec)``.
|
|
|
|
|
|
.. 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.
|
|
|
|
|
|
.. 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.
|
|
|
|
This function is added to the built-in namespace by the :mod:`site` module.
|
|
|
|
|
|
.. function:: hex(x)
|
|
|
|
Convert an integer number to a hexadecimal string. The result is a valid Python
|
|
expression. If *x* is not a Python :class:`int` object, it has to define an
|
|
:meth:`__index__` method that returns an integer.
|
|
|
|
|
|
.. function:: id(object)
|
|
|
|
Return the "identity" of an object. This is an integer which
|
|
is guaranteed to be unique and constant for this object during its lifetime.
|
|
Two objects with non-overlapping lifetimes may have the same :func:`id` value.
|
|
(Implementation note: this is the address of the object.)
|
|
|
|
|
|
.. function:: input([prompt])
|
|
|
|
If the *prompt* argument is present, it is written to standard output without
|
|
a trailing newline. The function then reads a line from input, converts it
|
|
to a string (stripping a trailing newline), and returns that. When EOF is
|
|
read, :exc:`EOFError` is raised. Example::
|
|
|
|
>>> s = input('--> ')
|
|
--> Monty Python's Flying Circus
|
|
>>> s
|
|
"Monty Python's Flying Circus"
|
|
|
|
If the :mod:`readline` module was loaded, then :func:`input` will use it
|
|
to provide elaborate line editing and history features.
|
|
|
|
|
|
.. function:: int([number | string[, radix]])
|
|
|
|
Convert a number or string to an integer. If no arguments are given, return
|
|
``0``. If a number is given, return ``number.__int__()``. Conversion of
|
|
floating point numbers to integers truncates towards zero. A string must be
|
|
a base-radix integer literal optionally preceded by '+' or '-' (with no space
|
|
in between) and optionally surrounded by whitespace. A base-n literal
|
|
consists of the digits 0 to n-1, with 'a' to 'z' (or 'A' to 'Z') having
|
|
values 10 to 35. The default radix is 10. The allowed values are 0 and 2-36.
|
|
Base-2, -8, and -16 literals can be optionally prefixed with ``0b``/``0B``,
|
|
``0o``/``0O``, or ``0x``/``0X``, as with integer literals in code. Radix 0
|
|
means to interpret exactly as a code literal, so that the actual radix is 2,
|
|
8, 10, or 16, and so that ``int('010', 0)`` is not legal, while
|
|
``int('010')`` is, as well as ``int('010', 8)``.
|
|
|
|
The integer type is described in :ref:`typesnumeric`.
|
|
|
|
|
|
.. 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. If *object* is not
|
|
an object of the given type, the function always returns false. If
|
|
*classinfo* is not a class (type object), it may be a tuple of type objects,
|
|
or may recursively contain other such tuples (other sequence types are not
|
|
accepted). If *classinfo* is not a type or tuple of types and such tuples,
|
|
a :exc:`TypeError` exception is raised.
|
|
|
|
|
|
.. function:: issubclass(class, classinfo)
|
|
|
|
Return true if *class* is a subclass (direct 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.
|
|
|
|
|
|
.. function:: iter(o[, sentinel])
|
|
|
|
Return an :term:`iterator` object. The first argument is interpreted very differently
|
|
depending on the presence of the second argument. Without a second argument, *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.
|
|
|
|
|
|
.. 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`.
|
|
|
|
.. 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 :func:`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:: map(function, iterable, ...)
|
|
|
|
Return an iterator that applies *function* to every item of *iterable*,
|
|
yielding the results. If additional *iterable* arguments are passed,
|
|
*function* must take that many arguments and is applied to the items from all
|
|
iterables in parallel. With multiple iterables, the iterator stops when the
|
|
shortest iterable is exhausted.
|
|
|
|
|
|
.. 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 keyword-only *key* argument specifies a one-argument ordering
|
|
function like that used for :meth:`list.sort`.
|
|
|
|
|
|
.. function:: memoryview(obj)
|
|
:noindex:
|
|
|
|
Return a "memory view" object created from the given argument. See
|
|
:ref:`typememoryview` for more information.
|
|
|
|
|
|
.. 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 keyword-only *key* argument specifies a one-argument ordering
|
|
function like that used for :meth:`list.sort`.
|
|
|
|
|
|
.. function:: next(iterator[, default])
|
|
|
|
Retrieve the next item from the *iterator* by calling its :meth:`__next__`
|
|
method. If *default* is given, it is returned if the iterator is exhausted,
|
|
otherwise :exc:`StopIteration` is raised.
|
|
|
|
|
|
.. function:: object()
|
|
|
|
Return a new featureless object. :class:`object` is a base for all classes.
|
|
It has the methods that are common to all instances of Python classes. This
|
|
function does not accept any arguments.
|
|
|
|
.. note::
|
|
|
|
:class:`object` does *not* have a :attr:`__dict__`, so you can't assign
|
|
arbitrary attributes to an instance of the :class:`object` class.
|
|
|
|
|
|
.. function:: oct(x)
|
|
|
|
Convert an integer number to an octal string. The result is a valid Python
|
|
expression. If *x* is not a Python :class:`int` object, it has to define an
|
|
:meth:`__index__` method that returns an integer.
|
|
|
|
|
|
.. function:: open(file[, mode='r'[, buffering=None[, encoding=None[, errors=None[, newline=None[, closefd=True]]]]]])
|
|
|
|
Open a file. If the file cannot be opened, :exc:`IOError` is raised.
|
|
|
|
*file* is either a string or bytes object giving the name (and the path if
|
|
the file isn't in the current working directory) of the file to be opened or
|
|
an integer file descriptor of the file to be wrapped. (If a file descriptor
|
|
is given, it is closed when the returned I/O object is closed, unless
|
|
*closefd* is set to ``False``.)
|
|
|
|
*mode* is an optional string that specifies the mode in which the file is
|
|
opened. It defaults to ``'r'`` which means open for reading in text mode.
|
|
Other common values are ``'w'`` for writing (truncating the file if it
|
|
already exists), and ``'a'`` for appending (which on *some* Unix systems,
|
|
means that *all* writes append to the end of the file regardless of the
|
|
current seek position). In text mode, if *encoding* is not specified the
|
|
encoding used is platform dependent. (For reading and writing raw bytes use
|
|
binary mode and leave *encoding* unspecified.) The available modes are:
|
|
|
|
========= ===============================================================
|
|
Character Meaning
|
|
--------- ---------------------------------------------------------------
|
|
``'r'`` open for reading (default)
|
|
``'w'`` open for writing, truncating the file first
|
|
``'a'`` open for writing, appending to the end of the file if it exists
|
|
``'b'`` binary mode
|
|
``'t'`` text mode (default)
|
|
``'+'`` open a disk file for updating (reading and writing)
|
|
``'U'`` universal newline mode (for backwards compatibility; unneeded
|
|
for new code)
|
|
========= ===============================================================
|
|
|
|
The default mode is ``'rt'`` (open for reading text). For binary random
|
|
access, the mode ``'w+b'`` opens and truncates the file to 0 bytes, while
|
|
``'r+b'`` opens the file without truncation.
|
|
|
|
Python distinguishes between files opened in binary and text modes, even
|
|
when the underlying operating system doesn't. Files opened in binary
|
|
mode (appending ``'b'`` to the *mode* argument) return contents as
|
|
``bytes`` objects without any decoding. In text mode (the default, or when
|
|
``'t'`` is appended to the *mode* argument) the contents of
|
|
the file are returned as strings, the bytes having been first decoded
|
|
using a platform-dependent encoding or using the specified *encoding*
|
|
if given.
|
|
|
|
*buffering* is an optional integer used to set the buffering policy. By
|
|
default full buffering is on. Pass 0 to switch buffering off (only allowed in
|
|
binary mode), 1 to set line buffering, and an integer > 1 for full buffering.
|
|
|
|
*encoding* is the name of the encoding used to decode or encode the file.
|
|
This should only be used in text mode. The default encoding is platform
|
|
dependent, but any encoding supported by Python can be passed. See the
|
|
:mod:`codecs` module for the list of supported encodings.
|
|
|
|
*errors* is an optional string that specifies how encoding errors are to be
|
|
handled---this argument should not be used in binary mode. Pass ``'strict'``
|
|
to raise a :exc:`ValueError` exception if there is an encoding error (the
|
|
default of ``None`` has the same effect), or pass ``'ignore'`` to ignore
|
|
errors. (Note that ignoring encoding errors can lead to data loss.) See the
|
|
documentation for :func:`codecs.register` for a list of the permitted
|
|
encoding error strings.
|
|
|
|
*newline* controls how universal newlines works (it only applies to text
|
|
mode). It can be ``None``, ``''``, ``'\n'``, ``'\r'``, and ``'\r\n'``. It
|
|
works as follows:
|
|
|
|
* On input, if *newline* is ``None``, universal newlines mode is enabled.
|
|
Lines in the input can end in ``'\n'``, ``'\r'``, or ``'\r\n'``, and these
|
|
are translated into ``'\n'`` before being returned to the caller. If it is
|
|
``''``, universal newline mode is enabled, but line endings are returned to
|
|
the caller untranslated. If it has any of the other legal values, input
|
|
lines are only terminated by the given string, and the line ending is
|
|
returned to the caller untranslated.
|
|
|
|
* On output, if *newline* is ``None``, any ``'\n'`` characters written are
|
|
translated to the system default line separator, :data:`os.linesep`. If
|
|
*newline* is ``''``, no translation takes place. If *newline* is any of
|
|
the other legal values, any ``'\n'`` characters written are translated to
|
|
the given string.
|
|
|
|
If *closefd* is ``False``, the underlying file descriptor will be kept open
|
|
when the file is closed. This does not work when a file name is given and
|
|
must be ``True`` in that case.
|
|
|
|
.. index::
|
|
single: line-buffered I/O
|
|
single: unbuffered I/O
|
|
single: buffer size, I/O
|
|
single: I/O control; buffering
|
|
single: binary mode
|
|
single: text mode
|
|
module: sys
|
|
|
|
See also the file handling modules, such as, :mod:`fileinput`, :mod:`io`
|
|
(where :func:`open()` is declared), :mod:`os`, :mod:`os.path`,
|
|
:mod:`tempfile`, and :mod:`shutil`.
|
|
|
|
|
|
.. XXX works for bytes too, but should it?
|
|
.. function:: ord(c)
|
|
|
|
Given a string of length one, return an integer representing the Unicode code
|
|
point of the character. For example, ``ord('a')`` returns the integer ``97``
|
|
and ``ord('\u2020')`` returns ``8224``. This is the inverse of :func:`chr`.
|
|
|
|
If the argument length is not one, a :exc:`TypeError` will be raised. (If
|
|
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!)
|
|
|
|
|
|
.. function:: pow(x, y[, z])
|
|
|
|
Return *x* to the power *y*; if *z* is present, return *x* to the power *y*,
|
|
modulo *z* (computed more efficiently than ``pow(x, y) % z``). The two-argument
|
|
form ``pow(x, y)`` is equivalent to using the power operator: ``x**y``.
|
|
|
|
The arguments must have numeric types. With mixed operand types, the
|
|
coercion rules for binary arithmetic operators apply. For :class:`int`
|
|
operands, the result has the same type as the operands (after coercion)
|
|
unless the second argument is negative; in that case, all arguments are
|
|
converted to float and a float result is delivered. For example, ``10**2``
|
|
returns ``100``, but ``10**-2`` returns ``0.01``. If the second argument is
|
|
negative, the third argument must be omitted. If *z* is present, *x* and *y*
|
|
must be of integer types, and *y* must be non-negative.
|
|
|
|
|
|
.. function:: print([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 :func:`str` does and
|
|
written to the stream, separated by *sep* and followed by *end*. Both *sep*
|
|
and *end* must be strings; they can also be ``None``, which means to use the
|
|
default values. If no *object* is given, :func:`print` will just write
|
|
*end*.
|
|
|
|
The *file* argument must be an object with a ``write(string)`` method; if it
|
|
is not present or ``None``, :data:`sys.stdout` will be used.
|
|
|
|
|
|
.. function:: property([fget[, fset[, fdel[, doc]]]])
|
|
|
|
Return a property attribute.
|
|
|
|
*fget* is a function for getting an attribute value, likewise *fset* is a
|
|
function for setting, and *fdel* a function for del'ing, an attribute. Typical
|
|
use is to define a managed attribute x::
|
|
|
|
class C(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 :term:`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.
|
|
|
|
A property object has :attr:`getter`, :attr:`setter`, and :attr:`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.
|
|
|
|
|
|
.. XXX does accept objects with __index__ too
|
|
.. function:: range([start,] stop[, step])
|
|
|
|
This is a versatile function to create iterables yielding arithmetic
|
|
progressions. It is most often used in :keyword:`for` loops. The arguments
|
|
must be integers. If the *step* argument is omitted, it defaults to ``1``.
|
|
If the *start* argument is omitted, it defaults to ``0``. The full form
|
|
returns an iterable of integers ``[start, start + step, start + 2 * step,
|
|
...]``. If *step* is positive, the last element is the largest ``start + i *
|
|
step`` less than *stop*; if *step* is negative, the last element is the
|
|
smallest ``start + i * step`` greater than *stop*. *step* must not be zero
|
|
(or else :exc:`ValueError` is raised). Example:
|
|
|
|
>>> list(range(10))
|
|
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
|
|
>>> list(range(1, 11))
|
|
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
|
|
>>> list(range(0, 30, 5))
|
|
[0, 5, 10, 15, 20, 25]
|
|
>>> list(range(0, 10, 3))
|
|
[0, 3, 6, 9]
|
|
>>> list(range(0, -10, -1))
|
|
[0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
|
|
>>> list(range(0))
|
|
[]
|
|
>>> list(range(1, 0))
|
|
[]
|
|
|
|
|
|
.. function:: repr(object)
|
|
|
|
Return a string containing a printable representation of an object. For many
|
|
types, this function makes an attempt to return a string that would yield an
|
|
object with the same value when passed to :func:`eval`, otherwise the
|
|
representation is a string enclosed in angle brackets that contains the name
|
|
of the type of the object together with additional information often
|
|
including the name and address of the object. A class can control what this
|
|
function returns for its instances by defining a :meth:`__repr__` method.
|
|
|
|
|
|
.. function:: reversed(seq)
|
|
|
|
Return a reverse :term:`iterator`. *seq* must be an object which has
|
|
a :meth:`__reversed__` method or supports the sequence protocol (the
|
|
:meth:`__len__` method and the :meth:`__getitem__` method with integer
|
|
arguments starting at ``0``).
|
|
|
|
|
|
.. function:: round(x[, n])
|
|
|
|
Return the floating point value *x* rounded to *n* digits after the decimal
|
|
point. If *n* is omitted, it defaults to zero. Delegates to
|
|
``x.__round__(n)``.
|
|
|
|
For the built-in types supporting :func:`round`, values are rounded to the
|
|
closest multiple of 10 to the power minus *n*; if two multiples are equally
|
|
close, rounding is done toward the even choice (so, for example, both
|
|
``round(0.5)`` and ``round(-0.5)`` are ``0``, and ``round(1.5)`` is ``2``).
|
|
The return value is an integer if called with one argument, otherwise of the
|
|
same type as *x*.
|
|
|
|
|
|
.. function:: set([iterable])
|
|
:noindex:
|
|
|
|
Return a new set, optionally with elements are taken from *iterable*.
|
|
The set type is described in :ref:`types-set`.
|
|
|
|
|
|
.. 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 :term:`slice` object representing the set of indices specified by
|
|
``range(start, stop, step)``. The *start* and *step* arguments default to
|
|
``None``. Slice objects have read-only data attributes :attr:`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[, key[, reverse]])
|
|
|
|
Return a new sorted list from the items in *iterable*.
|
|
|
|
Has two optional arguments which must be specified as keyword arguments.
|
|
|
|
*key* specifies a function of one argument that is used to extract a comparison
|
|
key from each list element: ``key=str.lower``. The default value is ``None``.
|
|
|
|
*reverse* is a boolean value. If set to ``True``, then the list elements are
|
|
sorted as if each comparison were reversed.
|
|
|
|
|
|
.. function:: staticmethod(function)
|
|
|
|
Return a static method for *function*.
|
|
|
|
A static method does not receive an implicit first argument. To declare a static
|
|
method, use this idiom::
|
|
|
|
class C:
|
|
@staticmethod
|
|
def f(arg1, arg2, ...): ...
|
|
|
|
The ``@staticmethod`` form is a function :term:`decorator` -- see the
|
|
description of function definitions in :ref:`function` for details.
|
|
|
|
It can be called either on the class (such as ``C.f()``) or on an instance (such
|
|
as ``C().f()``). The instance is ignored except for its class.
|
|
|
|
Static methods in Python are similar to those found in Java or C++. 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`.
|
|
|
|
|
|
.. function:: str([object[, encoding[, errors]]])
|
|
|
|
Return a string version of an object, using one of the following modes:
|
|
|
|
If *encoding* and/or *errors* are given, :func:`str` will decode the
|
|
*object* which can either be a byte 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.
|
|
|
|
When only *object* is given, this returns its nicely printable representation.
|
|
For strings, this is 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.
|
|
With no arguments, this returns the empty string.
|
|
|
|
Objects can specify what ``str(object)`` returns by defining a :meth:`__str__`
|
|
special method.
|
|
|
|
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,
|
|
see the :ref:`string-formatting` section. In addition see the
|
|
:ref:`stringservices` section.
|
|
|
|
|
|
.. 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)``.
|
|
|
|
|
|
.. function:: super([type[, object-or-type]])
|
|
|
|
Return a *super* object that acts as a proxy to superclasses 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.
|
|
Calling :func:`super` without arguments is equivalent to ``super(this_class,
|
|
first_arg)``.
|
|
|
|
There are two typical use cases for :func:`super`. In a class hierarchy with
|
|
single inheritance, :func:`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 inheritence 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 in 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 parent calls is determined at runtime and because that order adapts
|
|
to changes in the class hierarchy).
|
|
|
|
For both use cases, a typical superclass call looks like this::
|
|
|
|
class C(B):
|
|
def method(self, arg):
|
|
super().method(arg) # This does the same thing as: super(C, self).method(arg)
|
|
|
|
Note that :func:`super` is implemented as part of the binding process for
|
|
explicit dotted attribute lookups such as ``super().__getitem__(name)``.
|
|
It does so by implementing its own :meth:`__getattribute__` method for searching
|
|
parent classes in a predictable order that supports cooperative multiple inheritance.
|
|
Accordingly, :func:`super` is undefined for implicit lookups using statements or
|
|
operators such as ``super()[name]``.
|
|
|
|
Also note that :func:`super` is not limited to use inside methods. The
|
|
two argument specifies the arguments exactly and makes the appropriate
|
|
references. The zero argument form automatically searches the stack frame
|
|
for the class (``__class__``) and the first argument.
|
|
|
|
|
|
.. 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`.
|
|
|
|
|
|
.. function:: type(object)
|
|
|
|
.. index:: object: type
|
|
|
|
Return the type of an *object*. The return value is a type object and
|
|
generally the same object as returned by ``object.__class__``.
|
|
|
|
The :func:`isinstance` built-in function is recommended for testing the type
|
|
of an object, because it takes subclasses into account.
|
|
|
|
With three arguments, :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))
|
|
|
|
|
|
.. 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:: zip(*iterables)
|
|
|
|
Make an iterator that aggregates elements from each of the iterables.
|
|
|
|
Returns an iterator of tuples, where the *i*-th tuple contains
|
|
the *i*-th element from each of the argument sequences or iterables. The
|
|
iterator stops when the shortest input iterable is exhausted. With a single
|
|
iterable argument, it returns an iterator of 1-tuples. With no arguments,
|
|
it returns an empty iterator. Equivalent to::
|
|
|
|
def zip(*iterables):
|
|
# zip('ABCD', 'xy') --> Ax By
|
|
iterables = map(iter, iterables)
|
|
while iterables:
|
|
result = [it.next() for it in iterables]
|
|
yield tuple(result)
|
|
|
|
The left-to-right evaluation order of the iterables is guaranteed. This
|
|
makes possible an idiom for clustering a data series into n-length groups
|
|
using ``zip(*[iter(s)]*n)``.
|
|
|
|
:func:`zip` should only be used with unequal length inputs when you don't
|
|
care about trailing, unmatched values from the longer iterables. If those
|
|
values are important, use :func:`itertools.zip_longest` instead.
|
|
|
|
:func:`zip` in conjunction with the ``*`` operator can be used to unzip a
|
|
list::
|
|
|
|
>>> x = [1, 2, 3]
|
|
>>> y = [4, 5, 6]
|
|
>>> zipped = zip(x, y)
|
|
>>> list(zipped)
|
|
[(1, 4), (2, 5), (3, 6)]
|
|
>>> x2, y2 = zip(*zip(x, y))
|
|
>>> x == x2, y == y2
|
|
True
|
|
|
|
|
|
.. function:: __import__(name[, globals[, locals[, fromlist[, level]]]])
|
|
|
|
.. index::
|
|
statement: import
|
|
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. See 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 :term:`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__`.
|
|
|
|
|
|
.. rubric:: Footnotes
|
|
|
|
.. [#] 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.
|
|
|