f | |
| .. _built-in-funcs: |
| |
| Built-in Functions |
| ================== |
| |
| The Python interpreter has a number of functions built into it that are always |
| available. They are listed here in alphabetical order. |
n | |
| |
| .. function:: __import__(name[, globals[, locals[, fromlist[, level]]]]) |
| |
| .. index:: |
| statement: import |
| module: ihooks |
| module: rexec |
| module: imp |
| |
| This function is invoked by the :keyword:`import` statement. It mainly exists |
| so that you can replace it with another function that has a compatible |
| interface, in order to change the semantics of the :keyword:`import` statement. |
| For examples of why and how you would do this, see the standard library modules |
| :mod:`ihooks` and :mod:`rexec`. See also the built-in module :mod:`imp`, which |
| defines some useful operations out of which you can build your own |
| :func:`__import__` function. |
| |
| For example, the statement ``import spam`` results in the following call: |
| ``__import__('spam',`` ``globals(),`` ``locals(), [], -1)``; the statement |
| ``from spam.ham import eggs`` results in ``__import__('spam.ham', globals(), |
| locals(), ['eggs'], -1)``. Note that even though ``locals()`` and ``['eggs']`` |
| are passed in as arguments, the :func:`__import__` function does not set the |
| local variable named ``eggs``; this is done by subsequent code that is generated |
| for the import statement. (In fact, the standard implementation does not use |
| its *locals* argument at all, and uses its *globals* only to determine the |
| package context of the :keyword:`import` statement.) |
| |
| When the *name* variable is of the form ``package.module``, normally, the top- |
| level package (the name up till the first dot) is returned, *not* the module |
| named by *name*. However, when a non-empty *fromlist* argument is given, the |
| module named by *name* is returned. This is done for compatibility with the |
| bytecode generated for the different kinds of import statement; when using |
| ``import spam.ham.eggs``, the top-level package :mod:`spam` must be placed in |
| the importing namespace, but when using ``from spam.ham import eggs``, the |
| ``spam.ham`` subpackage must be used to find the ``eggs`` variable. As a |
| workaround for this behavior, use :func:`getattr` to extract the desired |
| components. For example, you could define the following helper:: |
| |
| def my_import(name): |
| mod = __import__(name) |
| components = name.split('.') |
| for comp in components[1:]: |
| mod = getattr(mod, comp) |
| return mod |
| |
| *level* specifies whether to use absolute or relative imports. The default is |
| ``-1`` which indicates both absolute and relative imports will be attempted. |
| ``0`` means only perform absolute imports. Positive values for *level* indicate |
| the number of parent directories to search relative to the directory of the |
| module calling :func:`__import__`. |
| |
| .. versionchanged:: 2.5 |
| The level parameter was added. |
| |
| .. versionchanged:: 2.5 |
| Keyword support for parameters was added. |
| |
| |
| .. function:: abs(x) |
| |
| Return the absolute value of a number. The argument may be a plain or long |
| integer or a floating point number. If the argument is a complex number, its |
| magnitude is returned. |
| |
| .. versionadded:: 2.2.1 |
| |
| .. versionchanged:: 2.3 |
| If no argument is given, this function returns :const:`False`. |
| |
| |
| .. function:: callable(object) |
| |
n | Return true if the *object* argument appears callable, false if not. If this |
n | Return :const:`True` if the *object* argument appears callable, |
| :const:`False` if not. If this |
| returns true, it is still possible that a call fails, but if it is false, |
| calling *object* will never succeed. Note that classes are callable (calling a |
| class returns a new instance); class instances are callable if they have a |
| :meth:`__call__` method. |
| |
| |
| .. function:: chr(i) |
| |
| Return a string of one character whose ASCII code is the integer *i*. For |
| example, ``chr(97)`` returns the string ``'a'``. This is the inverse of |
| :func:`ord`. The argument must be in the range [0..255], inclusive; |
n | :exc:`ValueError` will be raised if *i* is outside that range. |
n | :exc:`ValueError` will be raised if *i* is outside that range. See |
| also :func:`unichr`. |
| |
| |
| .. function:: classmethod(function) |
| |
| Return a class method for *function*. |
| |
| A class method receives the class as implicit first argument, just like an |
| instance method receives the instance. To declare a class method, use this |
| idiom:: |
| |
| class C: |
| @classmethod |
| def f(cls, arg1, arg2, ...): ... |
| |
n | The ``@classmethod`` form is a function decorator -- see the description of |
n | The ``@classmethod`` form is a function :term:`decorator` -- see the description |
| function definitions in chapter 7 of the Python Reference Manual (XXX reference: |
| of function definitions in :ref:`function` for details. |
| ../ref/ref.html) 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 |
n | type hierarchy in chapter 3 of the Python Reference Manual (XXX reference: |
n | type hierarchy in :ref:`types`. |
| ../ref/types.html) (at the bottom). |
| |
| .. versionadded:: 2.2 |
| |
| .. versionchanged:: 2.4 |
| Function decorator syntax added. |
| |
| |
| .. function:: cmp(x, y) |
| |
| Compare the two objects *x* and *y* and return an integer according to the |
| outcome. The return value is negative if ``x < y``, zero if ``x == y`` and |
| strictly positive if ``x > y``. |
| |
| |
n | .. function:: compile(string, filename, kind[, flags[, dont_inherit]]) |
n | .. function:: compile(source, filename, mode[, flags[, dont_inherit]]) |
| |
n | Compile the *string* into a code object. Code objects can be executed by an |
n | Compile the *source* into a code or AST object. Code objects can be executed |
| :keyword:`exec` statement or evaluated by a call to :func:`eval`. The |
| 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. |
| |
| *filename* argument should give the file from which the code was read; pass some |
| The *filename* argument should give the file from which the code was read; |
| recognizable value if it wasn't read from a file (``'<string>'`` is commonly |
| pass some recognizable value if it wasn't read from a file (``'<string>'`` is |
| commonly used). |
| |
| used). The *kind* argument specifies what kind of code must be compiled; it can |
| The *mode* argument specifies what kind of code must be compiled; it can be |
| be ``'exec'`` if *string* consists of a sequence of statements, ``'eval'`` if it |
| ``'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 |
n | interactive statement (in the latter case, expression statements that evaluate |
n | interactive statement (in the latter case, expression statements that |
| to something else than ``None`` will be printed). |
| evaluate to something else than ``None`` will be printed). |
| |
n | When compiling multi-line statements, two caveats apply: line endings must be |
| represented by a single newline character (``'\n'``), and the input must be |
| terminated by at least one newline character. If line endings are represented |
| by ``'\r\n'``, use the string :meth:`replace` method to change them into |
| ``'\n'``. |
| |
| The optional arguments *flags* and *dont_inherit* (which are new in Python 2.2) |
| The optional arguments *flags* and *dont_inherit* control which future |
| control which future statements (see :pep:`236`) affect the compilation of |
| statements (see :pep:`236`) affect the compilation of *source*. If neither |
| *string*. If neither is present (or both are zero) the code is compiled with |
| is present (or both are zero) the code is compiled with those future |
| those future statements that are in effect in the code that is calling compile. |
| statements that are in effect in the code that is calling compile. If the |
| If the *flags* argument is given and *dont_inherit* is not (or is zero) then 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 |
n | the *flags* argument is it -- the future statements in effect around the call to |
n | the *flags* argument is it -- the future statements in effect around the call |
| compile are ignored. |
| to compile are ignored. |
| |
n | Future statements are specified by bits which can be bitwise or-ed together to |
n | 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. |
n | |
| 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'``. |
| |
| .. versionchanged:: 2.3 |
| The *flags* and *dont_inherit* arguments were added. |
| |
| .. versionchanged:: 2.6 |
| Support for compiling AST objects. |
| |
| |
| .. function:: complex([real[, imag]]) |
| |
| Create a complex number with the value *real* + *imag*\*j or convert a string or |
| number to a complex number. If the first parameter is a string, it will be |
| interpreted as a complex number and the function must be called without a second |
| parameter. The second parameter can never be a string. Each argument may be any |
| numeric type (including complex). If *imag* is omitted, it defaults to zero and |
| the function serves as a numeric conversion function like :func:`int`, |
| :func:`long` and :func:`float`. If both arguments are omitted, returns ``0j``. |
| |
n | 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``. |
| |
| |
n | .. function:: dict([mapping-or-sequence]) |
n | .. function:: dict([arg]) |
| :noindex: |
| |
n | Return a new dictionary initialized from an optional positional argument or from |
n | Create a new data dictionary, optionally with items taken from *arg*. |
| a set of keyword arguments. If no arguments are given, return a new empty |
| The dictionary type is described in :ref:`typesmapping`. |
| dictionary. If the positional argument is a mapping object, return a dictionary |
| mapping the same keys to the same values as does the mapping object. Otherwise |
| the positional argument must be a sequence, a container that supports iteration, |
| or an iterator object. The elements of the argument must each also be of one of |
| those kinds, and each must in turn contain exactly two objects. The first is |
| used as a key in the new dictionary, and the second as the key's value. If a |
| given key is seen more than once, the last value associated with it is retained |
| in the new dictionary. |
| |
n | If keyword arguments are given, the keywords themselves with their associated |
n | For other containers see the built in :class:`list`, :class:`set`, and |
| values are added as items to the dictionary. If a key is specified both in the |
| :class:`tuple` classes, and the :mod:`collections` module. |
| positional argument and as a keyword argument, the value associated with the |
| keyword is retained in the dictionary. For example, these all return a |
| dictionary equal to ``{"one": 2, "two": 3}``: |
| |
| * ``dict({'one': 2, 'two': 3})`` |
| |
| * ``dict({'one': 2, 'two': 3}.items())`` |
| |
| * ``dict({'one': 2, 'two': 3}.iteritems())`` |
| |
| * ``dict(zip(('one', 'two'), (2, 3)))`` |
| |
| * ``dict([['two', 3], ['one', 2]])`` |
| |
| * ``dict(one=2, two=3)`` |
| |
| * ``dict([(['one', 'two'][i-2], i) for i in (2, 3)])`` |
| |
| .. versionadded:: 2.2 |
| |
| .. versionchanged:: 2.3 |
| Support for building a dictionary from keyword arguments added. |
| |
| |
| .. function:: dir([object]) |
| |
n | Without arguments, return the list of names in the current local symbol table. |
n | Without arguments, return the list of names in the current local scope. With an |
| With an argument, attempts to return a list of valid attributes for that object. |
| 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 |
| This information is gleaned from the object's :attr:`__dict__` attribute, if |
| gather information from the object's :attr:`__dict__` attribute, if defined, and |
| defined, and from the class or type object. The list is not necessarily |
| 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: |
| |
| complete. If the object is a module object, the list contains the names of the |
| * If the object is a module object, the list contains the names of the module's |
| attributes. |
| |
| module's attributes. If the object is a type or class object, the list contains |
| * If the object is a type or class object, the list contains the names of its |
| the names of its attributes, and recursively of the attributes of its bases. |
| attributes, and recursively of the attributes of its bases. |
| |
| Otherwise, the list contains the object's attributes' names, the names of its |
| * 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 |
| class's attributes, and recursively of the attributes of its class's base |
| classes. |
| |
| classes. The resulting list is sorted alphabetically. For example:: |
| The resulting list is sorted alphabetically. For example: |
| |
| >>> import struct |
n | >>> dir() |
n | >>> dir() # doctest: +SKIP |
| ['__builtins__', '__doc__', '__name__', 'struct'] |
n | >>> 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(struct) |
| >>> dir(f) |
| ['__doc__', '__name__', 'calcsize', 'error', 'pack', 'unpack'] |
| ['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 |
n | detailed behavior may change across releases. |
n | 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 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 |
| but may be 1 less than that. In any case ``q * b + a % b`` is very close to |
| *a*, if ``a % b`` is non-zero it has the same sign as *b*, and ``0 <= abs(a % b) |
| < abs(b)``. |
| |
| .. versionchanged:: 2.3 |
| Using :func:`divmod` with complex numbers is deprecated. |
| |
| |
n | .. function:: enumerate(iterable) |
n | .. function:: enumerate(sequence[, start=0]) |
| |
n | Return an enumerate object. *iterable* must be a sequence, an iterator, or some |
n | Return an enumerate object. *sequence* must be a sequence, an |
| other object which supports iteration. The :meth:`next` method of the iterator |
| :term:`iterator`, or some other object which supports iteration. The |
| returned by :func:`enumerate` returns a tuple containing a count (from zero) and |
| :meth:`next` method of the iterator returned by :func:`enumerate` returns a |
| tuple containing a count (from *start* which defaults to 0) and the |
| the corresponding value obtained from iterating over *iterable*. |
| corresponding value obtained from iterating over *iterable*. |
| :func:`enumerate` is useful for obtaining an indexed series: ``(0, seq[0])``, |
n | ``(1, seq[1])``, ``(2, seq[2])``, .... |
n | ``(1, seq[1])``, ``(2, seq[2])``, .... For example: |
| |
| >>> for i, season in enumerate(['Spring', 'Summer', 'Fall', 'Winter']): |
| ... print i, season |
| 0 Spring |
| 1 Summer |
| 2 Fall |
| 3 Winter |
| |
| .. versionadded:: 2.3 |
n | .. versionadded:: 2.6 |
| The *start* parameter. |
| |
| |
| .. function:: eval(expression[, globals[, locals]]) |
| |
| The arguments are a string and optional globals and locals. If provided, |
| *globals* must be a dictionary. If provided, *locals* can be any mapping |
| object. |
| |
| .. versionchanged:: 2.4 |
| formerly *locals* was required to be a dictionary. |
| |
| The *expression* argument is parsed and evaluated as a Python expression |
| (technically speaking, a condition list) using the *globals* and *locals* |
n | dictionaries as global and local name space. If the *globals* dictionary is |
n | 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:`__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 |
n | environment where :keyword:`eval` is called. The return value is the result of |
n | environment where :func:`eval` is called. The return value is the result of |
| the evaluated expression. Syntax errors are reported as exceptions. Example:: |
| the evaluated expression. Syntax errors are reported as exceptions. Example: |
| |
| >>> x = 1 |
| >>> print eval('x+1') |
| 2 |
| |
n | This function can also be used to execute arbitrary code objects (such as those |
n | This function can also be used to execute arbitrary code objects (such as |
| created by :func:`compile`). In this case pass a code object instead of a |
| those created by :func:`compile`). In this case pass a code object instead |
| string. The code object must have been compiled passing ``'eval'`` as the |
| of a string. If the code object has been compiled with ``'exec'`` as the |
| *kind* argument. |
| *kind* argument, :func:`eval`\'s return value will be ``None``. |
| |
| Hints: dynamic execution of statements is supported by the :keyword:`exec` |
| statement. Execution of statements from a file is supported by the |
| :func:`execfile` function. The :func:`globals` and :func:`locals` functions |
| returns the current global and local dictionary, respectively, which may be |
| useful to pass around for use by :func:`eval` or :func:`execfile`. |
| |
| |
| modifications to the default *locals* dictionary should not be attempted. Pass |
| an explicit *locals* dictionary if you need to see effects of the code on |
| *locals* after function :func:`execfile` returns. :func:`execfile` cannot be |
| used reliably to modify a function's locals. |
| |
| |
| .. function:: file(filename[, mode[, bufsize]]) |
| |
n | Constructor function for the :class:`file` type, described further in section |
n | Constructor function for the :class:`file` type, described further in section |
| :ref:`bltin-file-objects`, "File Objects (XXX reference: bltin-file- |
| objects.html)". The constructor's arguments are the same as those of the |
| :ref:`bltin-file-objects`. The constructor's arguments are the same as those |
| :func:`open` built-in function described below. |
| of the :func:`open` built-in function described below. |
| |
| When opening a file, it's preferable to use :func:`open` instead of invoking |
| this constructor directly. :class:`file` is more suited to type testing (for |
| example, writing ``isinstance(f, file)``). |
| |
| .. versionadded:: 2.2 |
| |
| |
n | .. function:: filter(function, list) |
n | .. function:: filter(function, iterable) |
| |
n | Construct a list from those elements of *list* for which *function* returns |
n | Construct a list from those elements of *iterable* for which *function* returns |
| true. *list* may be either a sequence, a container which supports iteration, or |
| true. *iterable* may be either a sequence, a container which supports |
| an iterator, If *list* is a string or a tuple, the result also has that type; |
| iteration, or an iterator. If *iterable* is a string or a tuple, the result |
| otherwise it is always a list. If *function* is ``None``, the identity function |
| also has that type; otherwise it is always a list. If *function* is ``None``, |
| is assumed, that is, all elements of *list* that are false are removed. |
| the identity function is assumed, that is, all elements of *iterable* that are |
| false are removed. |
| |
n | Note that ``filter(function, list)`` is equivalent to ``[item for item in list |
n | Note that ``filter(function, iterable)`` is equivalent to ``[item for item in |
| if function(item)]`` if function is not ``None`` and ``[item for item in list if |
| iterable if function(item)]`` if function is not ``None`` and ``[item for item |
| item]`` if function is ``None``. |
| in iterable if item]`` if function is ``None``. |
| |
| See :func:`itertools.filterfalse` for the complementary function that returns |
| elements of *iterable* for which *function* returns false. |
| |
| |
| .. function:: float([x]) |
| |
| 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 |
n | embedded in whitespace. The argument may also be [+|-]nan or [+|-]inf. |
| embedded in whitespace. Otherwise, the argument may be a plain or long integer |
| Otherwise, the argument may be a plain or long integer |
| or a floating point number, and a floating point number with the same value |
| (within Python's floating point precision) is returned. If no argument is |
| given, returns ``0.0``. |
| |
| .. note:: |
| |
| .. index:: |
| single: NaN |
| single: Infinity |
| |
| When passing in a string, values for NaN and Infinity may be returned, depending |
n | on the underlying C library. The specific set of strings accepted which cause |
n | on the underlying C library. Float accepts the strings nan, inf and -inf for |
| these values to be returned depends entirely on the C library and is known to |
| NaN and positive or negative infinity. The case and a leading + are ignored as |
| vary. |
| 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 *value* to a "formatted" representation, as controlled by |
| *format_spec*. The interpretation of *format_spec* will depend on the type |
| of the *value* argument, however there is a standard formatting syntax that |
| is used by most built-in types: :ref:`formatspec`. |
| |
| .. note:: |
| |
| ``format(value, format_spec)`` merely calls |
| ``value.__format__(format_spec)``. |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. function:: frozenset([iterable]) |
n | :noindex: |
| |
n | Return a frozenset object whose elements are taken from *iterable*. Frozensets |
n | Return a frozenset object, optionally with elements taken from *iterable*. |
| are sets that have no update methods but can be hashed and used as members of |
| The frozenset type is described in :ref:`types-set`. |
| other sets or as dictionary keys. The elements of a frozenset must be immutable |
| |
| themselves. To represent sets of sets, the inner sets should also be |
| For other containers see the built in :class:`dict`, :class:`list`, and |
| :class:`frozenset` objects. If *iterable* is not specified, returns a new empty |
| :class:`tuple` classes, and the :mod:`collections` module. |
| set, ``frozenset([])``. |
| |
| .. versionadded:: 2.4 |
| |
| |
| .. function:: getattr(object, name[, default]) |
| |
| Return the value of the named attributed of *object*. *name* must be a string. |
| If the string is the name of one of the object's attributes, the result is the |
| If the :mod:`readline` module was loaded, then :func:`input` will use it to |
| provide elaborate line editing and history features. |
| |
| Consider using the :func:`raw_input` function for general input from users. |
| |
| |
| .. function:: int([x[, radix]]) |
| |
n | Convert a string or number to a plain integer. If the argument is a string, it |
n | Convert a string or number to a plain integer. If the argument is a string, |
| must contain a possibly signed decimal number representable as a Python integer, |
| it must contain a possibly signed decimal number representable as a Python |
| possibly embedded in whitespace. The *radix* parameter gives the base for the |
| integer, possibly embedded in whitespace. The *radix* parameter gives the |
| conversion and may be any integer in the range [2, 36], or zero. If *radix* is |
| base for the conversion (which is 10 by default) and may be any integer in |
| zero, the proper radix is guessed based on the contents of string; the |
| the range [2, 36], or zero. If *radix* is zero, the proper radix is |
| interpretation is the same as for integer literals. If *radix* is specified and |
| determined based on the contents of string; the interpretation is the same as |
| for integer literals. (See :ref:`numbers`.) If *radix* is specified and *x* |
| *x* is not a string, :exc:`TypeError` is raised. Otherwise, the argument may be |
| is not a string, :exc:`TypeError` is raised. Otherwise, the argument may be a |
| a plain or long integer or a floating point number. Conversion of floating |
| plain or long integer or a floating point number. Conversion of floating |
| point numbers to integers truncates (towards zero). If the argument is outside |
| point numbers to integers truncates (towards zero). If the argument is |
| the integer range a long object will be returned instead. If no arguments are |
| outside the integer range a long object will be returned instead. If no |
| given, returns ``0``. |
| arguments are given, returns ``0``. |
| |
| The integer type is described in :ref:`typesnumeric`. |
| |
| |
| .. function:: isinstance(object, classinfo) |
| |
| Return true if the *object* argument is an instance of the *classinfo* argument, |
| or of a (direct or indirect) subclass thereof. Also return true if *classinfo* |
n | is a type object and *object* is an object of that type. If *object* is not a |
n | is a type object (new-style class) and *object* is an object of that type or of |
| class instance or an object of the given type, the function always returns |
| a (direct or indirect) subclass thereof. If *object* is not a class instance or |
| false. If *classinfo* is neither a class object nor a type object, it may be a |
| an object of the given type, the function always returns false. If *classinfo* |
| tuple of class or type objects, or may recursively contain other such tuples |
| is neither a class object nor a type object, it may be a tuple of class or type |
| (other sequence types are not accepted). If *classinfo* is not a class, type, |
| objects, or may recursively contain other such tuples (other sequence types are |
| or tuple of classes, types, and such tuples, a :exc:`TypeError` exception is |
| not accepted). If *classinfo* is not a class, type, or tuple of classes, types, |
| raised. |
| and such tuples, a :exc:`TypeError` exception is raised. |
| |
| .. versionchanged:: 2.2 |
| Support for a tuple of type information was added. |
| |
| |
| .. function:: issubclass(class, classinfo) |
| |
| Return true if *class* is a subclass (direct or indirect) of *classinfo*. A |
| |
| |
| .. 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). |
| |
| |
n | .. function:: list([sequence]) |
n | .. function:: list([iterable]) |
| |
n | Return a list whose items are the same and in the same order as *sequence*'s |
n | Return a list whose items are the same and in the same order as *iterable*'s |
| items. *sequence* may be either a sequence, a container that supports |
| items. *iterable* may be either a sequence, a container that supports |
| iteration, or an iterator object. If *sequence* is already a list, a copy is |
| iteration, or an iterator object. If *iterable* is already a list, a copy is |
| made and returned, similar to ``sequence[:]``. For instance, ``list('abc')`` |
| 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, ``[]``. |
| |
n | :class:`list` is a mutable sequence type, as documented in |
| :ref:`typesseq`. For other containers see the built in :class:`dict`, |
| :class:`set`, and :class:`tuple` classes, and the :mod:`collections` module. |
| |
| |
| .. function:: locals() |
| |
| Update and return a dictionary representing the current local symbol table. |
| |
| .. warning:: |
| |
| The contents of this dictionary should not be modified; changes may not affect |
| the values of local variables used by the interpreter. |
n | |
| 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:: long([x[, radix]]) |
| |
| Convert a string or number to a long integer. If the argument is a string, it |
| must contain a possibly signed number of arbitrary size, possibly embedded in |
| whitespace. The *radix* argument is interpreted in the same way as for |
| :func:`int`, and may only be given when *x* is a string. Otherwise, the argument |
| may be a plain or long integer or a floating point number, and a long integer |
| with the same value is returned. Conversion of floating point numbers to |
| integers truncates (towards zero). If no arguments are given, returns ``0L``. |
| |
n | The long type is described in :ref:`typesnumeric`. |
| |
n | .. function:: map(function, list, ...) |
n | .. function:: map(function, iterable, ...) |
| |
n | Apply *function* to every item of *list* and return a list of the results. If |
n | Apply *function* to every item of *iterable* and return a list of the results. |
| additional *list* arguments are passed, *function* must take that many arguments |
| If additional *iterable* arguments are passed, *function* must take that many |
| and is applied to the items of all lists in parallel; if a list is shorter than |
| arguments and is applied to the items from all iterables in parallel. If one |
| another it is assumed to be extended with ``None`` items. If *function* is |
| iterable is shorter than another it is assumed to be extended with ``None`` |
| ``None``, the identity function is assumed; if there are multiple list |
| items. If *function* is ``None``, the identity function is assumed; if there |
| arguments, :func:`map` returns a list consisting of tuples containing the |
| are multiple arguments, :func:`map` returns a list consisting of tuples |
| corresponding items from all lists (a kind of transpose operation). The *list* |
| containing the corresponding items from all iterables (a kind of transpose |
| arguments may be any kind of sequence; the result is always a list. |
| operation). The *iterable* arguments may be a sequence or any iterable object; |
| the result is always a list. |
| |
| |
n | .. function:: max(s[, args...][key]) |
n | .. function:: max(iterable[, args...][key]) |
| |
n | With a single argument *s*, return the largest item of a non-empty sequence |
n | With a single argument *iterable*, return the largest item of a non-empty |
| (such as a string, tuple or list). With more than one argument, return the |
| iterable (such as a string, tuple or list). With more than one argument, return |
| largest of the arguments. |
| the largest of the arguments. |
| |
| The optional *key* argument specifies a one-argument ordering function like that |
| used for :meth:`list.sort`. The *key* argument, if supplied, must be in keyword |
| form (for example, ``max(a,b,c,key=func)``). |
| |
| .. versionchanged:: 2.5 |
| Added support for the optional *key* argument. |
| |
| |
n | .. function:: min(s[, args...][key]) |
n | .. function:: min(iterable[, args...][key]) |
| |
n | With a single argument *s*, return the smallest item of a non-empty sequence |
n | With a single argument *iterable*, return the smallest item of a non-empty |
| (such as a string, tuple or list). With more than one argument, return the |
| iterable (such as a string, tuple or list). With more than one argument, return |
| smallest of the arguments. |
| the smallest of the arguments. |
| |
| The optional *key* argument specifies a one-argument ordering function like that |
| used for :meth:`list.sort`. The *key* argument, if supplied, must be in keyword |
| form (for example, ``min(a,b,c,key=func)``). |
| |
| .. versionchanged:: 2.5 |
| Added support for the optional *key* argument. |
| |
| |
n | .. 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. |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. function:: object() |
| |
| Return a new featureless object. :class:`object` is a base for all new style |
| classes. It has the methods that are common to all instances of new style |
| classes. |
| |
| .. versionadded:: 2.2 |
| |
| 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.) |
| |
| |
n | .. 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. |
| |
| .. note:: |
| |
| This function is not normally available as a builtin since the name |
| ``print`` is recognized as the :keyword:`print` statement. To disable the |
| statement and use the :func:`print` function, use this future statement at |
| the top of your module:: |
| |
| from __future__ import print_function |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. function:: property([fget[, fset[, fdel[, doc]]]]) |
| |
n | Return a property attribute for new-style classes (classes that derive from |
n | Return a property attribute for :term:`new-style class`\es (classes that |
| :class:`object`). |
| derive from :class:`object`). |
| |
| *fget* is a function for getting an attribute value, likewise *fset* is a |
| function for setting, and *fdel* a function for del'ing, an attribute. Typical |
| use is to define a managed attribute x:: |
| |
| class C(object): |
n | def __init__(self): self.__x = None |
n | def __init__(self): |
| self._x = None |
| |
| def getx(self): return self._x |
| def getx(self): |
| return self._x |
| def setx(self, value): self._x = value |
| def setx(self, value): |
| self._x = value |
| def delx(self): del self._x |
| 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 |
n | create read-only properties easily using :func:`property` as a decorator:: |
n | 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 |
| |
n | turns the :meth:`voltage` method into a "getter" for a read-only attribute with |
n | turns the :meth:`voltage` method into a "getter" for a read-only attribute |
| the same name. |
| 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. |
| |
| .. versionadded:: 2.2 |
| |
| .. versionchanged:: 2.5 |
| Use *fget*'s docstring if no *doc* given. |
n | |
| .. versionchanged:: 2.6 |
| The ``getter``, ``setter``, and ``deleter`` attributes were added. |
| |
| |
| .. function:: range([start,] stop[, step]) |
| |
| This is a versatile function to create lists containing arithmetic progressions. |
| It is most often used in :keyword:`for` loops. The arguments must be plain |
| integers. If the *step* argument is omitted, it defaults to ``1``. If the |
| *start* argument is omitted, it defaults to ``0``. The full form returns a list |
| of plain integers ``[start, start + step, start + 2 * step, ...]``. If *step* |
| is positive, the last element is the largest ``start + i * step`` less than |
| *stop*; if *step* is negative, the last element is the smallest ``start + i * |
| step`` greater than *stop*. *step* must not be zero (or else :exc:`ValueError` |
n | is raised). Example:: |
n | 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) |
| --> Monty Python's Flying Circus |
| >>> s |
| "Monty Python's Flying Circus" |
| |
| If the :mod:`readline` module was loaded, then :func:`raw_input` will use it to |
| provide elaborate line editing and history features. |
| |
| |
n | .. function:: reduce(function, sequence[, initializer]) |
n | .. function:: reduce(function, iterable[, initializer]) |
| |
n | Apply *function* of two arguments cumulatively to the items of *sequence*, from |
n | Apply *function* of two arguments cumulatively to the items of *iterable*, from |
| left to right, so as to reduce the sequence to a single value. For example, |
| 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 |
n | the update value from the *sequence*. If the optional *initializer* is present, |
n | the update value from the *iterable*. If the optional *initializer* is present, |
| it is placed before the items of the sequence in the calculation, and serves as |
| it is placed before the items of the iterable in the calculation, and serves as |
| a default when the sequence is empty. If *initializer* is not given and |
| a default when the iterable is empty. If *initializer* is not given and |
| *sequence* contains only one item, the first item is returned. |
| *iterable* contains only one item, the first item is returned. |
| |
| |
| .. function:: reload(module) |
| |
| Reload a previously imported *module*. The argument must be a module object, so |
| it must have been successfully imported before. This is useful if you have |
| edited the module source file using an external editor and want to try out the |
| new version without leaving the Python interpreter. The return value is the |
| module object (the same as the *module* argument). |
| |
| When ``reload(module)`` is executed: |
| |
n | * Python modules' code is recompiled and the module-level code reexecuted, |
n | * 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. |
| |
n | * As with all other objects in Python the old objects are only reclaimed after |
n | * As with all other objects in Python the old objects are only reclaimed after |
| their reference counts drop to zero. |
| |
n | * The names in the module namespace are updated to point to any new or changed |
n | * The names in the module namespace are updated to point to any new or changed |
| objects. |
| |
n | * Other references to the old objects (such as names external to the module) are |
n | * Other references to the old objects (such as names external to the module) are |
| not rebound to refer to the new objects and must be updated in each namespace |
| where they occur if that is desired. |
| |
| There are a number of other caveats: |
| |
| If a module is syntactically correct but its initialization fails, the first |
| :keyword:`import` statement for it does not bind its name locally, but does |
| store a (partially initialized) module object in ``sys.modules``. To reload the |
| |
| If a module instantiates instances of a class, reloading the module that defines |
| the class does not affect the method definitions of the instances --- they |
| continue to use the old class definition. The same is true for derived classes. |
| |
| |
| .. function:: repr(object) |
| |
n | Return a string containing a printable representation of an object. This is the |
n | Return a string containing a printable representation of an object. This is |
| same value yielded by conversions (reverse quotes). It is sometimes useful to be |
| the same value yielded by conversions (reverse quotes). It is sometimes |
| able to access this operation as an ordinary function. For many types, this |
| useful to be able to access this operation as an ordinary function. For many |
| function makes an attempt to return a string that would yield an object with the |
| types, this function makes an attempt to return a string that would yield an |
| same value when passed to :func:`eval`. |
| 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) |
| |
n | Return a reverse iterator. *seq* must be an object which supports the sequence |
n | Return a reverse :term:`iterator`. *seq* must be an object which has |
| a :meth:`__reversed__` method or supports the sequence protocol (the |
| protocol (the __len__() method and the :meth:`__getitem__` method with integer |
| :meth:`__len__` method and the :meth:`__getitem__` method with integer |
| arguments starting at ``0``). |
| |
| .. versionadded:: 2.4 |
n | |
| .. versionchanged:: 2.6 |
| Added the possibility to write a custom :meth:`__reversed__` method. |
| |
| |
| .. function:: round(x[, n]) |
| |
| Return the floating point value *x* rounded to *n* digits after the decimal |
| point. If *n* is omitted, it defaults to zero. The result is a floating point |
| number. Values are rounded to the closest multiple of 10 to the power minus |
| *n*; if two multiples are equally close, rounding is done away from 0 (so. for |
| example, ``round(0.5)`` is ``1.0`` and ``round(-0.5)`` is ``-1.0``). |
| |
| |
| .. function:: set([iterable]) |
n | :noindex: |
| |
n | Return a set whose elements are taken from *iterable*. The elements must be |
n | Return a new set, optionally with elements are taken from *iterable*. |
| immutable. To represent sets of sets, the inner sets should be |
| The set type is described in :ref:`types-set`. |
| :class:`frozenset` objects. If *iterable* is not specified, returns a new empty |
| |
| set, ``set([])``. |
| For other containers see the built in :class:`dict`, :class:`list`, and |
| :class:`tuple` classes, and the :mod:`collections` module. |
| |
| .. versionadded:: 2.4 |
| |
| |
| .. function:: setattr(object, name, value) |
| |
| This is the counterpart of :func:`getattr`. The arguments are an object, a |
| string and an arbitrary value. The string may name an existing attribute or a |
| object allows it. For example, ``setattr(x, 'foobar', 123)`` is equivalent to |
| ``x.foobar = 123``. |
| |
| |
| .. function:: slice([start,] stop[, step]) |
| |
| .. index:: single: Numerical Python |
| |
n | Return a slice object representing the set of indices specified by |
n | 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: |
n | ``a[start:stop:step]`` or ``a[start:stop, i]``. |
n | ``a[start:stop:step]`` or ``a[start:stop, i]``. See :func:`itertools.islice` |
| for an alternate version that returns an iterator. |
| |
| |
| .. function:: sorted(iterable[, cmp[, key[, reverse]]]) |
| |
| Return a new sorted list from the items in *iterable*. |
| |
| The optional arguments *cmp*, *key*, and *reverse* have the same meaning as |
| those for the :meth:`list.sort` method (described in section |
| :ref:`typesseq-mutable`). |
| |
| *cmp* specifies a custom comparison function of two arguments (iterable |
| elements) which should return a negative, zero or positive number depending on |
| whether the first argument is considered smaller than, equal to, or larger than |
n | the second argument: ``cmp=lambda x,y: cmp(x.lower(), y.lower())`` |
n | 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 |
n | key from each list element: ``key=str.lower`` |
n | 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. |
| |
n | In general, the *key* and *reverse* conversion processes are much faster than |
n | In general, the *key* and *reverse* conversion processes are much faster |
| specifying an equivalent *cmp* function. This is because *cmp* is called |
| than specifying an equivalent *cmp* function. This is because *cmp* is |
| multiple times for each list element while *key* and *reverse* touch each |
| called multiple times for each list element while *key* and *reverse* touch |
| element only once. |
| each element only once. To convert an old-style *cmp* function to a *key* |
| function, see the `CmpToKey recipe in the ASPN cookbook |
| <http://code.activestate.com/recipes/576653/>`_\. |
| |
| .. versionadded:: 2.4 |
| |
| |
| .. function:: staticmethod(function) |
| |
| Return a static method for *function*. |
| |
| A static method does not receive an implicit first argument. To declare a static |
| method, use this idiom:: |
| |
| class C: |
| @staticmethod |
| def f(arg1, arg2, ...): ... |
| |
n | The ``@staticmethod`` form is a function decorator -- see the description of |
n | The ``@staticmethod`` form is a function :term:`decorator` -- see the |
| function definitions in chapter 7 of the Python Reference Manual (XXX reference: |
| description of function definitions in :ref:`function` for details. |
| ../ref/function.html) 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 |
n | standard type hierarchy in chapter 3 of the Python Reference Manual (XXX |
n | standard type hierarchy in :ref:`types`. |
| reference: ../ref/types.html) (at the bottom). |
| |
| .. versionadded:: 2.2 |
| |
| .. versionchanged:: 2.4 |
| Function decorator syntax added. |
| |
| |
| .. function:: str([object]) |
| |
| Return a string containing a nicely printable representation of an object. For |
| strings, this returns the string itself. The difference with ``repr(object)`` |
| is that ``str(object)`` does not always attempt to return a string that is |
| acceptable to :func:`eval`; its goal is to return a printable string. If no |
| argument is given, returns the empty string, ``''``. |
| |
n | For more information on strings see :ref:`typesseq` which describes sequence |
| functionality (strings are sequences), and also the string-specific methods |
| described in the :ref:`string-methods` section. To output formatted strings |
| use template strings or the ``%`` operator described in the |
| :ref:`string-formatting` section. In addition see the :ref:`stringservices` |
| section. See also :func:`unicode`. |
| |
n | |
| .. function:: sum(sequence[, start]) |
| .. function:: sum(iterable[, start]) |
| |
n | Sums *start* and the items of a *sequence*, from left to right, and returns the |
n | Sums *start* and the items of an *iterable* from left to right and returns the |
| total. *start* defaults to ``0``. The *sequence*'s items are normally numbers, |
| 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 |
| 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)`` |
n | To add floating point values with extended precision, see :func:`math.fsum`\. |
| |
| .. versionadded:: 2.3 |
| |
| |
| .. function:: super(type[, object-or-type]) |
| |
n | Return the superclass of *type*. If the second argument is omitted the super |
n | Return a proxy object that delegates method calls to a parent or sibling |
| object returned is unbound. If the second argument is an object, |
| class of *type*. This is useful for accessing inherited methods that have |
| ``isinstance(obj, type)`` must be true. If the second argument is a type, |
| been overridden in a class. The search order is same as that used by |
| ``issubclass(type2, type)`` must be true. :func:`super` only works for new-style |
| :func:`getattr` except that the *type* itself is skipped. |
| classes. |
| |
n | A typical use for calling a cooperative superclass method is:: |
n | The :attr:`__mro__` attribute of the *type* lists the method resolution |
| search order used by both :func:`getattr` and :func:`super`. The attribute |
| is dynamic and can change whenever the inheritance hierarchy is updated. |
| |
| If the second argument is omitted, the super object returned is unbound. If |
| the second argument is an object, ``isinstance(obj, type)`` must be true. If |
| the second argument is a type, ``issubclass(type2, type)`` must be true (this |
| is useful for classmethods). |
| |
| .. note:: |
| :func:`super` only works for :term:`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): |
n | def meth(self, arg): |
n | def method(self, arg): |
| super(C, self).meth(arg) |
| super(C, self).method(arg) |
| |
| Note that :func:`super` is implemented as part of the binding process for |
n | explicit dotted attribute lookups such as ``super(C, self).__getitem__(name)``. |
n | explicit dotted attribute lookups such as ``super().__getitem__(name)``. |
| It does so by implementing its own :meth:`__getattribute__` method for searching |
| classes in a predictable order that supports cooperative multiple inheritance. |
| Accordingly, :func:`super` is undefined for implicit lookups using statements or |
n | operators such as ``super(C, self)[name]``. |
n | operators such as ``super()[name]``. |
| |
| Also note that :func:`super` is not limited to use inside methods. The two |
| argument form specifies the arguments exactly and makes the appropriate |
| references. |
| |
| .. versionadded:: 2.2 |
| |
| |
n | .. function:: tuple([sequence]) |
n | .. function:: tuple([iterable]) |
| |
n | Return a tuple whose items are the same and in the same order as *sequence*'s |
n | Return a tuple whose items are the same and in the same order as *iterable*'s |
| items. *sequence* may be a sequence, a container that supports iteration, or an |
| items. *iterable* may be a sequence, a container that supports iteration, or an |
| iterator object. If *sequence* is already a tuple, it is returned unchanged. |
| 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, ``()``. |
| |
n | :class:`tuple` is an immutable sequence type, as documented in |
| :ref:`typesseq`. For other containers see the built in :class:`dict`, |
| :class:`list`, and :class:`set` classes, and the :mod:`collections` module. |
| |
| |
| .. function:: type(object) |
| |
| .. index:: object: type |
| |
| Return the type of an *object*. The return value is a type object. The |
| :func:`isinstance` built-in function is recommended for testing the type of an |
| object. |
| |
| With three arguments, :func:`type` functions as a constructor as detailed below. |
| |
| |
| .. function:: type(name, bases, dict) |
n | :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 |
n | :class:`type` objects:: |
n | :class:`type` objects: |
| |
| >>> class X(object): |
| ... a = 1 |
n | ... |
n | ... |
| >>> X = type('X', (object,), dict(a=1)) |
| |
| .. versionadded:: 2.2 |
| |
| |
| .. function:: unichr(i) |
| |
| Return the Unicode string of one character whose Unicode code is the integer |
| *i*. For example, ``unichr(97)`` returns the string ``u'a'``. This is the |
| inverse of :func:`ord` for Unicode strings. The valid range for the argument |
| depends how Python was configured -- it may be either UCS2 [0..0xFFFF] or UCS4 |
n | [0..0x10FFFF]. :exc:`ValueError` is raised otherwise. |
n | [0..0x10FFFF]. :exc:`ValueError` is raised otherwise. For ASCII and 8-bit |
| strings see :func:`chr`. |
| |
| .. versionadded:: 2.0 |
| |
| |
| .. function:: unicode([object[, encoding [, errors]]]) |
| |
| Return the Unicode string version of *object* using one of the following modes: |
| |
| elements are never used (such as when the loop is usually terminated with |
| :keyword:`break`). |
| |
| .. note:: |
| |
| :func:`xrange` is intended to be simple and fast. Implementations may impose |
| restrictions to achieve this. The C implementation of Python restricts all |
| arguments to native C longs ("short" Python integers), and also requires that |
n | the number of elements fit in a native C long. |
n | the number of elements fit in a native C long. If a larger range is needed, |
| an alternate version can be crafted using the :mod:`itertools` module: |
| ``islice(count(start, step), (stop-start+step-1)//step)``. |
| |
| |
| .. function:: zip([iterable, ...]) |
| |
| This function returns a list of tuples, where the *i*-th tuple contains the |
| *i*-th element from each of the argument sequences or iterables. The returned |
| list is truncated in length to the length of the shortest argument sequence. |
| When there are multiple arguments which are all of the same length, :func:`zip` |
| is similar to :func:`map` with an initial argument of ``None``. With a single |
| sequence argument, it returns a list of 1-tuples. With no arguments, it returns |
| an empty list. |
| |
n | 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` 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 == x2, y == y2 |
| True |
| |
| .. versionadded:: 2.0 |
| |
| .. versionchanged:: 2.4 |
| Formerly, :func:`zip` required at least one argument and ``zip()`` raised a |
| :exc:`TypeError` instead of returning an empty list. |
| |
n | |
| .. 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. |
| |
| This function is invoked by the :keyword:`import` statement. It can be |
| replaced (by importing the :mod:`builtins` module and assigning to |
| ``builtins.__import__``) in order to change semantics of the |
| :keyword:`import` statement, but nowadays it is usually simpler to use import |
| hooks (see :pep:`302`). Direct use of :func:`__import__` is rare, except in |
| cases where you want to import a module whose name is only known at runtime. |
| |
| The function imports the module *name*, potentially using the given *globals* |
| and *locals* to determine how to interpret the name in a package context. |
| The *fromlist* gives the names of objects or submodules that should be |
| imported from the module given by *name*. The standard implementation does |
| not use its *locals* argument at all, and uses its *globals* only to |
| determine the package context of the :keyword:`import` statement. |
| |
| *level* specifies whether to use absolute or relative imports. 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__`. |
| |
| 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 :func:`__import__` returns the toplevel module here because this is |
| the object that is bound to a name by the :keyword:`import` statement. |
| |
| On the other hand, the statement ``from spam.ham import eggs, sausage as |
| saus`` results in :: |
| |
| _temp = __import__('spam.ham', globals(), locals(), ['eggs', 'sausage'], -1) |
| eggs = _temp.eggs |
| saus = _temp.sausage |
| |
| Here, the ``spam.ham`` module is returned from :func:`__import__`. From this |
| object, the names to import are retrieved and assigned to their respective |
| names. |
| |
| If you simply want to import a module (potentially within a package) by name, |
| you can get it from :data:`sys.modules`:: |
| |
| >>> import sys |
| >>> name = 'foo.bar.baz' |
| >>> __import__(name) |
| <module 'foo' from ...> |
| >>> baz = sys.modules[name] |
| >>> baz |
| <module 'foo.bar.baz' from ...> |
| |
| .. versionchanged:: 2.5 |
| The level parameter was added. |
| |
| .. versionchanged:: 2.5 |
| Keyword support for parameters was added. |
| |
| .. % --------------------------------------------------------------------------- |
| .. --------------------------------------------------------------------------- |
| |
| |
| .. _non-essential-built-in-funcs: |
| |
| Non-essential Built-in Functions |
| ================================ |
| |
| There are several built-in functions that are no longer essential to learn, know |
| or use in modern Python programming. They have been kept here to maintain |
| backwards compatibility with programs written for older versions of Python. |
| |
n | Python programmers, trainers, students and bookwriters should feel free to |
n | Python programmers, trainers, students and book writers should feel free to |
| bypass these functions without concerns about missing something important. |
| |
| |
| .. function:: apply(function, args[, keywords]) |
| |
| The *function* argument must be a callable object (a user-defined or built-in |
| function or method, or a class object) and the *args* argument must be a |
| sequence. The *function* is called with *args* as the argument list; the number |
| of arguments is the length of the tuple. If the optional *keywords* argument is |
| present, it must be a dictionary whose keys are strings. It specifies keyword |
| arguments to be added to the end of the argument list. Calling :func:`apply` is |
| different from just calling ``function(args)``, since in that case there is |
| always exactly one argument. The use of :func:`apply` is equivalent to |
n | ``function(*args, **keywords)``. Use of :func:`apply` is not necessary since the |
n | ``function(*args, **keywords)``. |
| "extended call syntax," as used in the last example, is completely equivalent. |
| |
| .. deprecated:: 2.3 |
t | Use the extended call syntax instead, as described above. |
t | Use the extended call syntax with ``*args`` and ``**keywords`` instead. |
| |
| |
| .. function:: buffer(object[, offset[, size]]) |
| |
| The *object* argument must be an object that supports the buffer call interface |
| (such as strings, arrays, and buffers). A new buffer object will be created |
| which references the *object* argument. The buffer object will be a slice from |
| the beginning of *object* (or from the specified *offset*). The slice will |