| |
| .. _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. |
| |
| =================== ================= ================== ================= ==================== |
| .. .. Built-in Functions .. .. |
| =================== ================= ================== ================= ==================== |
| :func:`abs` :func:`divmod` :func:`input` :func:`open` :func:`staticmethod` |
| :func:`all` :func:`enumerate` :func:`int` :func:`ord` :func:`str` |
| :func:`any` :func:`eval` :func:`isinstance` :func:`pow` :func:`sum` |
| :func:`basestring` :func:`execfile` :func:`issubclass` :func:`print` :func:`super` |
| :func:`bin` :func:`file` :func:`iter` :func:`property` :func:`tuple` |
| :func:`bool` :func:`filter` :func:`len` :func:`range` :func:`type` |
| :func:`bytearray` :func:`float` :func:`list` :func:`raw_input` :func:`unichr` |
| :func:`callable` :func:`format` :func:`locals` :func:`reduce` :func:`unicode` |
| :func:`chr` |func-frozenset|_ :func:`long` :func:`reload` :func:`vars` |
| :func:`classmethod` :func:`getattr` :func:`map` |func-repr|_ :func:`xrange` |
| :func:`cmp` :func:`globals` :func:`max` :func:`reversed` :func:`zip` |
| :func:`compile` :func:`hasattr` |func-memoryview|_ :func:`round` :func:`__import__` |
| :func:`complex` :func:`hash` :func:`min` |func-set|_ :func:`apply` |
| :func:`delattr` :func:`help` :func:`next` :func:`setattr` :func:`buffer` |
| |func-dict|_ :func:`hex` :func:`object` :func:`slice` :func:`coerce` |
| :func:`dir` :func:`id` :func:`oct` :func:`sorted` :func:`intern` |
| =================== ================= ================== ================= ==================== |
| |
| .. using :func:`dict` would create a link to another page, so local targets are |
| used, with replacement texts to make the output in the table consistent |
| |
| .. |func-dict| replace:: ``dict()`` |
| .. |func-frozenset| replace:: ``frozenset()`` |
| .. |func-memoryview| replace:: ``memoryview()`` |
| .. |func-repr| replace:: ``repr()`` |
| .. |func-set| replace:: ``set()`` |
| |
| |
| .. function:: abs(x) |
| |
| Return the absolute value of a number. The argument may be a plain or long |
| integer or a floating point number. If the argument is a complex number, its |
| magnitude is returned. |
| |
| |
| .. function:: all(iterable) |
| |
| Return True if all elements of the *iterable* are true (or if the iterable |
| is empty). Equivalent to:: |
| |
| def all(iterable): |
| for element in iterable: |
| if not element: |
| return False |
| return True |
| |
| .. versionadded:: 2.5 |
| |
| |
| .. function:: any(iterable) |
| |
| Return True if any element of the *iterable* is true. If the iterable |
| is empty, return False. Equivalent to:: |
| |
| def any(iterable): |
| for element in iterable: |
| if element: |
| return True |
| return False |
| |
| .. versionadded:: 2.5 |
| |
| |
| .. function:: basestring() |
| |
| This abstract type is the superclass for :class:`str` and :class:`unicode`. It |
| cannot be called or instantiated, but it can be used to test whether an object |
| is an instance of :class:`str` or :class:`unicode`. ``isinstance(obj, |
| basestring)`` is equivalent to ``isinstance(obj, (str, unicode))``. |
| |
| .. versionadded:: 2.3 |
| |
| |
| .. function:: 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. |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. function:: bool([x]) |
| |
| Convert a value to a Boolean, using the standard truth testing procedure. If |
| *x* is false or omitted, this returns :const:`False`; otherwise it returns |
| :const:`True`. :class:`bool` is also a class, which is a subclass of |
| :class:`int`. Class :class:`bool` cannot be subclassed further. Its only |
| instances are :const:`False` and :const:`True`. |
| |
| .. index:: pair: Boolean; type |
| |
| .. versionadded:: 2.2.1 |
| |
| .. versionchanged:: 2.3 |
| If no argument is given, this function returns :const:`False`. |
| |
| |
| .. function:: bytearray([source[, 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:`string-methods`. |
| |
| The optional *source* 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. |
| |
| .. versionadded:: 2.6 |
| |
| |
| .. function:: callable(object) |
| |
| Return :const:`True` if the *object* argument appears callable, |
| :const:`False` if not. If this |
| returns true, it is still possible that a call fails, but if it is false, |
| calling *object* will never succeed. Note that classes are callable (calling a |
| class returns a new instance); class instances are callable if they have a |
| :meth:`__call__` method. |
| |
| |
| .. function:: chr(i) |
| |
| Return a string of one character whose ASCII code is the integer *i*. For |
| example, ``chr(97)`` returns the string ``'a'``. This is the inverse of |
| :func:`ord`. The argument must be in the range [0..255], inclusive; |
| :exc:`ValueError` will be raised if *i* is outside that range. See |
| also :func:`unichr`. |
| |
| |
| .. function:: classmethod(function) |
| |
| Return a class method for *function*. |
| |
| A class method receives the class as implicit first argument, just like an |
| instance method receives the instance. To declare a class method, use this |
| idiom:: |
| |
| class C(object): |
| @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`. |
| |
| .. versionadded:: 2.2 |
| |
| .. versionchanged:: 2.4 |
| Function decorator syntax added. |
| |
| |
| .. function:: cmp(x, y) |
| |
| Compare the two objects *x* and *y* and return an integer according to the |
| outcome. The return value is negative if ``x < y``, zero if ``x == y`` and |
| strictly positive if ``x > y``. |
| |
| |
| .. function:: compile(source, filename, mode[, flags[, dont_inherit]]) |
| |
| Compile the *source* into a code 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 Unicode string, a *Latin-1* encoded 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 other than ``None`` will be printed). |
| |
| The optional arguments *flags* and *dont_inherit* control which future |
| statements (see :pep:`236`) affect the compilation of *source*. If neither |
| is present (or both are zero) the code is compiled with those future |
| statements that are in effect in the code that is calling compile. If the |
| *flags* argument is given and *dont_inherit* is not (or is zero) then the |
| future statements specified by the *flags* argument are used in addition to |
| those that would be used anyway. If *dont_inherit* is a non-zero integer then |
| the *flags* argument is it -- the future statements in effect around the call |
| to compile are ignored. |
| |
| Future statements are specified by bits which can be bitwise ORed together to |
| specify multiple statements. The bitfield required to specify a given feature |
| can be found as the :attr:`~__future__._Feature.compiler_flag` attribute on |
| the :class:`~__future__._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 code in ``'single'`` or |
| ``'eval'`` mode, input must be terminated by at least one newline |
| character. This is to facilitate detection of incomplete and complete |
| statements in the :mod:`code` module. |
| |
| .. versionchanged:: 2.3 |
| The *flags* and *dont_inherit* arguments were added. |
| |
| .. versionchanged:: 2.6 |
| Support for compiling AST objects. |
| |
| .. versionchanged:: 2.7 |
| Allowed use of Windows and Mac newlines. Also input in ``'exec'`` mode |
| does not have to end in a newline anymore. |
| |
| |
| .. 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``. |
| |
| .. note:: |
| |
| When converting from a string, the string must not contain whitespace |
| around the central ``+`` or ``-`` operator. For example, |
| ``complex('1+2j')`` is fine, but ``complex('1 + 2j')`` raises |
| :exc:`ValueError`. |
| |
| 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``. |
| |
| |
| .. _func-dict: |
| .. function:: dict(**kwarg) |
| dict(mapping, **kwarg) |
| dict(iterable, **kwarg) |
| :noindex: |
| |
| Create a new dictionary. The :class:`dict` object is the dictionary class. |
| See :class:`dict` and :ref:`typesmapping` for documentation about this |
| class. |
| |
| For other containers see the built-in :class:`list`, :class:`set`, and |
| :class:`tuple` classes, as well as 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() # show the names in the module namespace |
| ['__builtins__', '__doc__', '__name__', 'struct'] |
| >>> dir(struct) # show the names in the struct module |
| ['Struct', '__builtins__', '__doc__', '__file__', '__name__', |
| '__package__', '_clearcache', 'calcsize', 'error', 'pack', 'pack_into', |
| 'unpack', 'unpack_from'] |
| >>> class Shape(object): |
| def __dir__(self): |
| return ['area', 'perimeter', 'location'] |
| >>> s = Shape() |
| >>> dir(s) |
| ['area', 'perimeter', 'location'] |
| |
| .. 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 long division. With mixed |
| operand types, the rules for binary arithmetic operators apply. For plain and |
| long integers, the result is the same as ``(a // b, a % b)``. For floating point |
| numbers the result is ``(q, a % b)``, where *q* is usually ``math.floor(a / b)`` |
| but may be 1 less than that. In any case ``q * b + a % b`` is very close to |
| *a*, if ``a % b`` is non-zero it has the same sign as *b*, and ``0 <= abs(a % b) |
| < abs(b)``. |
| |
| .. versionchanged:: 2.3 |
| Using :func:`divmod` with complex numbers is deprecated. |
| |
| |
| .. function:: enumerate(sequence, start=0) |
| |
| Return an enumerate object. *sequence* 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 |
| values obtained from iterating over *sequence*:: |
| |
| >>> seasons = ['Spring', 'Summer', 'Fall', 'Winter'] |
| >>> list(enumerate(seasons)) |
| [(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')] |
| >>> list(enumerate(seasons, start=1)) |
| [(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')] |
| |
| Equivalent to:: |
| |
| def enumerate(sequence, start=0): |
| n = start |
| for elem in sequence: |
| yield n, elem |
| n += 1 |
| |
| .. versionadded:: 2.3 |
| .. versionchanged:: 2.6 |
| The *start* parameter was added. |
| |
| |
| .. function:: eval(expression[, globals[, locals]]) |
| |
| The arguments are a Unicode or *Latin-1* encoded string and optional |
| globals and locals. If provided, *globals* must be a dictionary. |
| If provided, *locals* can be any mapping object. |
| |
| .. versionchanged:: 2.4 |
| formerly *locals* was required to be a dictionary. |
| |
| The *expression* argument is parsed and evaluated as a Python expression |
| (technically speaking, a condition list) using the *globals* and *locals* |
| dictionaries as global and local 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 |
| 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 |
| >>> print eval('x+1') |
| 2 |
| |
| This function can also be used to execute arbitrary code objects (such as |
| those created by :func:`compile`). In this case pass a code object instead |
| of a string. If the code object has been compiled with ``'exec'`` as the |
| *mode* 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`. |
| |
| See :func:`ast.literal_eval` for a function that can safely evaluate strings |
| with expressions containing only literals. |
| |
| |
| .. function:: execfile(filename[, globals[, locals]]) |
| |
| This function is similar to the :keyword:`exec` statement, but parses a file |
| instead of a string. It is different from the :keyword:`import` statement in |
| that it does not use the module administration --- it reads the file |
| unconditionally and does not create a new module. [#]_ |
| |
| The arguments are a file name and two optional dictionaries. The file is parsed |
| and evaluated as a sequence of Python statements (similarly to a module) using |
| the *globals* and *locals* dictionaries as global and local namespace. If |
| provided, *locals* can be any mapping object. Remember that at module level, |
| globals and locals are the same dictionary. If two separate objects are |
| passed as *globals* and *locals*, the code will be executed as if it were |
| embedded in a class definition. |
| |
| .. versionchanged:: 2.4 |
| formerly *locals* was required to be a dictionary. |
| |
| If the *locals* dictionary is omitted it defaults to the *globals* dictionary. |
| If both dictionaries are omitted, the expression is executed in the environment |
| where :func:`execfile` is called. The return value is ``None``. |
| |
| .. note:: |
| |
| The default *locals* act as described for function :func:`locals` below: |
| modifications to the default *locals* dictionary should not be attempted. Pass |
| an explicit *locals* dictionary if you need to see effects of the code on |
| *locals* after function :func:`execfile` returns. :func:`execfile` cannot be |
| used reliably to modify a function's locals. |
| |
| |
| .. function:: file(name[, mode[, buffering]]) |
| |
| Constructor function for the :class:`file` type, described further in section |
| :ref:`bltin-file-objects`. The constructor's arguments are the same as those |
| of the :func:`open` built-in function described below. |
| |
| When opening a file, it's preferable to use :func:`open` instead of invoking |
| this constructor directly. :class:`file` is more suited to type testing (for |
| example, writing ``isinstance(f, file)``). |
| |
| .. versionadded:: 2.2 |
| |
| |
| .. function:: filter(function, iterable) |
| |
| Construct a list from those elements of *iterable* for which *function* returns |
| true. *iterable* may be either a sequence, a container which supports |
| iteration, or an iterator. If *iterable* is a string or a tuple, the result |
| also has that type; otherwise it is always a list. If *function* is ``None``, |
| the identity function is assumed, that is, all elements of *iterable* that are |
| false are removed. |
| |
| Note that ``filter(function, iterable)`` is equivalent to ``[item for item in |
| iterable if function(item)]`` if function is not ``None`` and ``[item for item |
| in iterable if item]`` if function is ``None``. |
| |
| See :func:`itertools.ifilter` and :func:`itertools.ifilterfalse` for iterator |
| versions of this function, including a variation that filters for elements |
| where the *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 |
| embedded in whitespace. The argument may also be [+|-]nan or [+|-]inf. |
| Otherwise, the argument may be a plain or long integer |
| or a floating point number, and a floating point number with the same value |
| (within Python's floating point precision) is returned. If no argument is |
| given, returns ``0.0``. |
| |
| .. note:: |
| |
| .. 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 *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 |
| |
| |
| .. _func-frozenset: |
| .. function:: frozenset([iterable]) |
| :noindex: |
| |
| Return a new :class:`frozenset` object, optionally with elements taken from |
| *iterable*. ``frozenset`` is a built-in class. See :class:`frozenset` and |
| :ref:`types-set` for documentation about this class. |
| |
| For other containers see the built-in :class:`set`, :class:`list`, |
| :class:`tuple`, and :class:`dict` classes, as well as the :mod:`collections` |
| module. |
| |
| .. versionadded:: 2.4 |
| |
| |
| .. function:: getattr(object, name[, default]) |
| |
| Return the value of the named attribute 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. |
| |
| .. versionadded:: 2.2 |
| |
| |
| .. function:: hex(x) |
| |
| Convert an integer number (of any size) to a hexadecimal string. The result is a |
| valid Python expression. |
| |
| .. note:: |
| |
| To obtain a hexadecimal string representation for a float, use the |
| :meth:`float.hex` method. |
| |
| .. versionchanged:: 2.4 |
| Formerly only returned an unsigned literal. |
| |
| |
| .. function:: id(object) |
| |
| Return the "identity" of an object. This is an integer (or long integer) which |
| is guaranteed to be unique and constant for this object during its lifetime. |
| Two objects with non-overlapping lifetimes may have the same :func:`id` |
| value. |
| |
| .. impl-detail:: This is the address of the object in memory. |
| |
| |
| .. function:: input([prompt]) |
| |
| Equivalent to ``eval(raw_input(prompt))``. |
| |
| This function does not catch user errors. If the input is not syntactically |
| valid, a :exc:`SyntaxError` will be raised. Other exceptions may be raised if |
| there is an error during evaluation. |
| |
| 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=0) |
| int(x, base=10) |
| |
| Convert a number or string *x* to an integer, or return ``0`` if no |
| arguments are given. If *x* is a number, it can be a plain integer, a long |
| integer, or a floating point number. If *x* is floating point, the conversion |
| truncates towards zero. If the argument is outside the integer range, the |
| function returns a long object instead. |
| |
| If *x* is not a number or if *base* is given, then *x* must be a string or |
| Unicode object representing an :ref:`integer literal <integers>` in radix |
| *base*. Optionally, the literal can be |
| preceded by ``+`` or ``-`` (with no space in between) and 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 *base* 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``/``0``, or ``0x``/``0X``, as with integer literals in code. |
| Base 0 means to interpret the string exactly as an integer literal, so that |
| the actual base is 2, 8, 10, or 16. |
| |
| 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, indirect or :term:`virtual <abstract base class>`) subclass |
| thereof. Also return true if *classinfo* |
| is a type object (new-style class) and *object* is an object of that type or of |
| a (direct, indirect or :term:`virtual <abstract base class>`) subclass |
| thereof. If *object* is not a class instance or |
| an object of the given type, the function always returns false. If *classinfo* |
| is neither a class object nor a type object, it may be a tuple of class or type |
| objects, or may recursively contain other such tuples (other sequence types are |
| not accepted). If *classinfo* is not a class, type, or tuple of classes, types, |
| and such tuples, a :exc:`TypeError` exception is raised. |
| |
| .. versionchanged:: 2.2 |
| Support for a tuple of type information was added. |
| |
| |
| .. function:: issubclass(class, classinfo) |
| |
| Return true if *class* is a subclass (direct, indirect or :term:`virtual |
| <abstract base class>`) of *classinfo*. A |
| class is considered a subclass of itself. *classinfo* may be a tuple of class |
| objects, in which case every entry in *classinfo* will be checked. In any other |
| case, a :exc:`TypeError` exception is raised. |
| |
| .. versionchanged:: 2.3 |
| Support for a tuple of type information was added. |
| |
| |
| .. function:: iter(o[, sentinel]) |
| |
| Return an :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:`~iterator.next` method; if the value returned is equal to *sentinel*, |
| :exc:`StopIteration` will be raised, otherwise the value will be returned. |
| |
| One useful application of the second form of :func:`iter` is to read lines of |
| a file until a certain line is reached. The following example reads a file |
| until the :meth:`~io.TextIOBase.readline` method returns an empty string:: |
| |
| with open('mydata.txt') as fp: |
| for line in iter(fp.readline, ''): |
| process_line(line) |
| |
| .. versionadded:: 2.2 |
| |
| |
| .. function:: len(s) |
| |
| Return the length (the number of items) of an object. The argument may be a |
| sequence (string, tuple or list) or a mapping (dictionary). |
| |
| |
| .. function:: list([iterable]) |
| |
| Return a list whose items are the same and in the same order as *iterable*'s |
| items. *iterable* may be either a sequence, a container that supports |
| iteration, or an iterator object. If *iterable* is already a list, a copy is |
| made and returned, similar to ``iterable[:]``. For instance, ``list('abc')`` |
| returns ``['a', 'b', 'c']`` and ``list( (1, 2, 3) )`` returns ``[1, 2, 3]``. If |
| no argument is given, returns a new empty list, ``[]``. |
| |
| :class:`list` is a mutable sequence type, as documented in |
| :ref:`typesseq`. For other containers see the built in :class:`dict`, |
| :class:`set`, and :class:`tuple` classes, and the :mod:`collections` module. |
| |
| |
| .. function:: locals() |
| |
| Update and return a dictionary representing the current local symbol table. |
| Free variables are returned by :func:`locals` when it is called in function |
| blocks, but not in class blocks. |
| |
| .. note:: |
| |
| The contents of this dictionary should not be modified; changes may not |
| affect the values of local and free variables used by the interpreter. |
| |
| |
| .. function:: long(x=0) |
| long(x, base=10) |
| |
| Convert a string or number to a long integer. If the argument is a string, it |
| must contain a possibly signed number of arbitrary size, possibly embedded in |
| whitespace. The *base* argument is interpreted in the same way as for |
| :func:`int`, and may only be given when *x* is a string. Otherwise, the argument |
| may be a plain or long integer or a floating point number, and a long integer |
| with the same value is returned. Conversion of floating point numbers to |
| integers truncates (towards zero). If no arguments are given, returns ``0L``. |
| |
| The long type is described in :ref:`typesnumeric`. |
| |
| |
| .. function:: map(function, iterable, ...) |
| |
| Apply *function* to every item of *iterable* and return a list of the results. |
| If additional *iterable* arguments are passed, *function* must take that many |
| arguments and is applied to the items from all iterables in parallel. If one |
| iterable is shorter than another it is assumed to be extended with ``None`` |
| items. If *function* is ``None``, the identity function is assumed; if there |
| are multiple arguments, :func:`map` returns a list consisting of tuples |
| containing the corresponding items from all iterables (a kind of transpose |
| operation). The *iterable* arguments may be a sequence or any iterable object; |
| the result is always a list. |
| |
| |
| .. function:: max(iterable[, key]) |
| max(arg1, arg2, *args[, key]) |
| |
| Return the largest item in an iterable or the largest of two or more |
| arguments. |
| |
| If one positional argument is provided, *iterable* must be a non-empty |
| iterable (such as a non-empty string, tuple or list). The largest item |
| in the iterable is returned. If two or more positional arguments are |
| provided, the largest of the positional arguments is returned. |
| |
| 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. |
| |
| .. _func-memoryview: |
| .. function:: memoryview(obj) |
| :noindex: |
| |
| Return a "memory view" object created from the given argument. See |
| :ref:`typememoryview` for more information. |
| |
| |
| .. function:: min(iterable[, key]) |
| min(arg1, arg2, *args[, key]) |
| |
| Return the smallest item in an iterable or the smallest of two or more |
| arguments. |
| |
| If one positional argument is provided, *iterable* must be a non-empty |
| iterable (such as a non-empty string, tuple or list). The smallest item |
| in the iterable is returned. If two or more positional arguments are |
| provided, the smallest of the positional arguments is returned. |
| |
| The optional *key* argument specifies a one-argument ordering function like that |
| used for :meth:`list.sort`. The *key* argument, if supplied, must be in keyword |
| form (for example, ``min(a,b,c,key=func)``). |
| |
| .. versionchanged:: 2.5 |
| Added support for the optional *key* argument. |
| |
| |
| .. function:: next(iterator[, default]) |
| |
| Retrieve the next item from the *iterator* by calling its |
| :meth:`~iterator.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 |
| |
| .. versionchanged:: 2.3 |
| This function does not accept any arguments. Formerly, it accepted arguments but |
| ignored them. |
| |
| |
| .. function:: oct(x) |
| |
| Convert an integer number (of any size) to an octal string. The result is a |
| valid Python expression. |
| |
| .. versionchanged:: 2.4 |
| Formerly only returned an unsigned literal. |
| |
| |
| .. function:: open(name[, mode[, buffering]]) |
| |
| Open a file, returning an object of the :class:`file` type described in |
| section :ref:`bltin-file-objects`. If the file cannot be opened, |
| :exc:`IOError` is raised. When opening a file, it's preferable to use |
| :func:`open` instead of invoking the :class:`file` constructor directly. |
| |
| The first two arguments are the same as for ``stdio``'s :c:func:`fopen`: |
| *name* is the file name to be opened, and *mode* is a string indicating how |
| the file is to be opened. |
| |
| The most commonly-used values of *mode* are ``'r'`` for reading, ``'w'`` for |
| writing (truncating the file if it already exists), and ``'a'`` for appending |
| (which on *some* Unix systems means that *all* writes append to the end of the |
| file regardless of the current seek position). If *mode* is omitted, it |
| defaults to ``'r'``. The default is to use text mode, which may convert |
| ``'\n'`` characters to a platform-specific representation on writing and back |
| on reading. Thus, when opening a binary file, you should append ``'b'`` to |
| the *mode* value to open the file in binary mode, which will improve |
| portability. (Appending ``'b'`` is useful even on systems that don't treat |
| binary and text files differently, where it serves as documentation.) See below |
| for more possible values of *mode*. |
| |
| .. index:: |
| single: line-buffered I/O |
| single: unbuffered I/O |
| single: buffer size, I/O |
| single: I/O control; buffering |
| |
| The optional *buffering* argument specifies the file's desired buffer size: 0 |
| means unbuffered, 1 means line buffered, any other positive value means use a |
| buffer of (approximately) that size (in bytes). A negative *buffering* means |
| to use the system default, which is usually line buffered for tty devices and |
| fully buffered for other files. If omitted, the system default is used. [#]_ |
| |
| Modes ``'r+'``, ``'w+'`` and ``'a+'`` open the file for updating (note that |
| ``'w+'`` truncates the file). Append ``'b'`` to the mode to open the file in |
| binary mode, on systems that differentiate between binary and text files; on |
| systems that don't have this distinction, adding the ``'b'`` has no effect. |
| |
| .. index:: |
| single: universal newlines; open() built-in function |
| |
| In addition to the standard :c:func:`fopen` values *mode* may be ``'U'`` or |
| ``'rU'``. Python is usually built with :term:`universal newlines` support; |
| supplying ``'U'`` opens the file as a text file, but lines may be terminated |
| by any of the following: the Unix end-of-line convention ``'\n'``, the |
| Macintosh convention ``'\r'``, or the Windows convention ``'\r\n'``. All of |
| these external representations are seen as ``'\n'`` by the Python program. |
| If Python is built without universal newlines support a *mode* with ``'U'`` |
| is the same as normal text mode. Note that file objects so opened also have |
| an attribute called :attr:`newlines` which has a value of ``None`` (if no |
| newlines have yet been seen), ``'\n'``, ``'\r'``, ``'\r\n'``, or a tuple |
| containing all the newline types seen. |
| |
| Python enforces that the mode, after stripping ``'U'``, begins with ``'r'``, |
| ``'w'`` or ``'a'``. |
| |
| Python provides many file handling modules including |
| :mod:`fileinput`, :mod:`os`, :mod:`os.path`, :mod:`tempfile`, and |
| :mod:`shutil`. |
| |
| .. versionchanged:: 2.5 |
| Restriction on first letter of mode string introduced. |
| |
| |
| .. function:: ord(c) |
| |
| Given a string of length one, return an integer representing the Unicode code |
| point of the character when the argument is a unicode object, or the value of |
| the byte when the argument is an 8-bit string. For example, ``ord('a')`` returns |
| the integer ``97``, ``ord(u'\u2020')`` returns ``8224``. This is the inverse of |
| :func:`chr` for 8-bit strings and of :func:`unichr` for unicode objects. If a |
| unicode argument is given and Python was built with UCS2 Unicode, then the |
| character's code point must be in the range [0..65535] inclusive; otherwise the |
| string length is two, and a :exc:`TypeError` will be raised. |
| |
| |
| .. function:: pow(x, y[, z]) |
| |
| Return *x* to the power *y*; if *z* is present, return *x* to the power *y*, |
| modulo *z* (computed more efficiently than ``pow(x, y) % z``). The two-argument |
| form ``pow(x, y)`` is equivalent to using the power operator: ``x**y``. |
| |
| The arguments must have numeric types. With mixed operand types, the coercion |
| rules for binary arithmetic operators apply. For int and long int operands, the |
| result has the same type as the operands (after coercion) unless the second |
| argument is negative; in that case, all arguments are converted to float and a |
| float result is delivered. For example, ``10**2`` returns ``100``, but |
| ``10**-2`` returns ``0.01``. (This last feature was added in Python 2.2. In |
| Python 2.1 and before, if both arguments were of integer types and the second |
| argument was negative, an exception was raised.) If the second argument is |
| negative, the third argument must be omitted. If *z* is present, *x* and *y* |
| must be of integer types, and *y* must be non-negative. (This restriction was |
| added in Python 2.2. In Python 2.1 and before, floating 3-argument ``pow()`` |
| returned platform-dependent results depending on floating-point rounding |
| accidents.) |
| |
| |
| .. function:: print(*objects, sep=' ', end='\\n', file=sys.stdout) |
| |
| Print *objects* 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 *objects* are 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. Output buffering |
| is determined by *file*. Use ``file.flush()`` to ensure, for instance, |
| immediate appearance on a screen. |
| |
| .. note:: |
| |
| This function is not normally available as a built-in 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]]]]) |
| |
| Return a property attribute for :term:`new-style class`\es (classes that |
| derive from :class:`object`). |
| |
| *fget* is a function for getting an attribute value, likewise *fset* is a |
| function for setting, and *fdel* a function for del'ing, an attribute. Typical |
| use is to define a managed attribute ``x``:: |
| |
| class C(object): |
| def __init__(self): |
| self._x = None |
| |
| def getx(self): |
| return self._x |
| def setx(self, value): |
| self._x = value |
| def delx(self): |
| del self._x |
| x = property(getx, setx, delx, "I'm the 'x' property.") |
| |
| If then *c* is an instance of *C*, ``c.x`` will invoke the getter, |
| ``c.x = value`` will invoke the setter and ``del c.x`` the deleter. |
| |
| If given, *doc* will be the docstring of the property attribute. Otherwise, the |
| property will copy *fget*'s docstring (if it exists). This makes it possible to |
| create read-only properties easily using :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:`~property.getter`, :attr:`~property.setter`, |
| and :attr:`~property.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. |
| |
| .. versionchanged:: 2.6 |
| The ``getter``, ``setter``, and ``deleter`` attributes were added. |
| |
| |
| .. function:: range(stop) |
| range(start, stop[, step]) |
| |
| This is a versatile function to create lists containing arithmetic progressions. |
| It is most often used in :keyword:`for` loops. The arguments must be plain |
| integers. If the *step* argument is omitted, it defaults to ``1``. If the |
| *start* argument is omitted, it defaults to ``0``. The full form returns a list |
| of plain integers ``[start, start + step, start + 2 * step, ...]``. If *step* |
| is positive, the last element is the largest ``start + i * step`` less than |
| *stop*; if *step* is negative, the last element is the smallest ``start + i * |
| step`` greater than *stop*. *step* must not be zero (or else :exc:`ValueError` |
| is raised). Example: |
| |
| >>> range(10) |
| [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] |
| >>> range(1, 11) |
| [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] |
| >>> range(0, 30, 5) |
| [0, 5, 10, 15, 20, 25] |
| >>> range(0, 10, 3) |
| [0, 3, 6, 9] |
| >>> range(0, -10, -1) |
| [0, -1, -2, -3, -4, -5, -6, -7, -8, -9] |
| >>> range(0) |
| [] |
| >>> range(1, 0) |
| [] |
| |
| |
| .. function:: raw_input([prompt]) |
| |
| If the *prompt* argument is present, it is written to standard output without a |
| trailing newline. The function then reads a line from input, converts it to a |
| string (stripping a trailing newline), and returns that. When EOF is read, |
| :exc:`EOFError` is raised. Example:: |
| |
| >>> s = raw_input('--> ') |
| --> Monty Python's Flying Circus |
| >>> s |
| "Monty Python's Flying Circus" |
| |
| If the :mod:`readline` module was loaded, then :func:`raw_input` will use it to |
| provide elaborate line editing and history features. |
| |
| |
| .. function:: reduce(function, iterable[, initializer]) |
| |
| Apply *function* of two arguments cumulatively to the items of *iterable*, from |
| left to right, so as to reduce the iterable to a single value. For example, |
| ``reduce(lambda x, y: x+y, [1, 2, 3, 4, 5])`` calculates ``((((1+2)+3)+4)+5)``. |
| The left argument, *x*, is the accumulated value and the right argument, *y*, is |
| the update value from the *iterable*. If the optional *initializer* is present, |
| it is placed before the items of the iterable in the calculation, and serves as |
| a default when the iterable is empty. If *initializer* is not given and |
| *iterable* contains only one item, the first item is returned. |
| Roughly equivalent to:: |
| |
| def reduce(function, iterable, initializer=None): |
| it = iter(iterable) |
| if initializer is None: |
| try: |
| initializer = next(it) |
| except StopIteration: |
| raise TypeError('reduce() of empty sequence with no initial value') |
| accum_value = initializer |
| for x in it: |
| accum_value = function(accum_value, x) |
| return accum_value |
| |
| .. function:: reload(module) |
| |
| Reload a previously imported *module*. The argument must be a module object, so |
| it must have been successfully imported before. This is useful if you have |
| edited the module source file using an external editor and want to try out the |
| new version without leaving the Python interpreter. The return value is the |
| module object (the same as the *module* argument). |
| |
| When ``reload(module)`` is executed: |
| |
| * Python modules' code is recompiled and the module-level code reexecuted, |
| defining a new set of objects which are bound to names in the module's |
| dictionary. The ``init`` function of extension modules is not called a second |
| time. |
| |
| * As with all other objects in Python the old objects are only reclaimed after |
| their reference counts drop to zero. |
| |
| * The names in the module namespace are updated to point to any new or changed |
| objects. |
| |
| * Other references to the old objects (such as names external to the module) are |
| not rebound to refer to the new objects and must be updated in each namespace |
| where they occur if that is desired. |
| |
| There are a number of other caveats: |
| |
| If a module is syntactically correct but its initialization fails, the first |
| :keyword:`import` statement for it does not bind its name locally, but does |
| store a (partially initialized) module object in ``sys.modules``. To reload the |
| module you must first :keyword:`import` it again (this will bind the name to the |
| partially initialized module object) before you can :func:`reload` it. |
| |
| When a module is reloaded, its dictionary (containing the module's global |
| variables) is retained. Redefinitions of names will override the old |
| definitions, so this is generally not a problem. If the new version of a module |
| does not define a name that was defined by the old version, the old definition |
| remains. This feature can be used to the module's advantage if it maintains a |
| global table or cache of objects --- with a :keyword:`try` statement it can test |
| for the table's presence and skip its initialization if desired:: |
| |
| try: |
| cache |
| except NameError: |
| cache = {} |
| |
| It is legal though generally not very useful to reload built-in or dynamically |
| loaded modules, except for :mod:`sys`, :mod:`__main__` and :mod:`__builtin__`. |
| In many cases, however, extension modules are not designed to be initialized |
| more than once, and may fail in arbitrary ways when reloaded. |
| |
| If a module imports objects from another module using :keyword:`from` ... |
| :keyword:`import` ..., calling :func:`reload` for the other module does not |
| redefine the objects imported from it --- one way around this is to re-execute |
| the :keyword:`from` statement, another is to use :keyword:`import` and qualified |
| names (*module*.*name*) instead. |
| |
| If a module instantiates instances of a class, reloading the module that defines |
| the class does not affect the method definitions of the instances --- they |
| continue to use the old class definition. The same is true for derived classes. |
| |
| |
| .. _func-repr: |
| .. function:: repr(object) |
| |
| Return a string containing a printable representation of an object. This is |
| the same value yielded by conversions (reverse quotes). It is sometimes |
| useful to be able to access this operation as an ordinary function. For many |
| types, this function makes an attempt to return a string that would yield an |
| object with the same value when passed to :func:`eval`, 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``). |
| |
| .. versionadded:: 2.4 |
| |
| .. versionchanged:: 2.6 |
| Added the possibility to write a custom :meth:`__reversed__` method. |
| |
| |
| .. function:: round(number[, ndigits]) |
| |
| Return the floating point value *number* rounded to *ndigits* digits after |
| the decimal point. If *ndigits* 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 *ndigits*; 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``). |
| |
| |
| .. note:: |
| |
| The behavior of :func:`round` for floats can be surprising: for example, |
| ``round(2.675, 2)`` gives ``2.67`` instead of the expected ``2.68``. |
| This is not a bug: it's a result of the fact that most decimal fractions |
| can't be represented exactly as a float. See :ref:`tut-fp-issues` for |
| more information. |
| |
| |
| .. _func-set: |
| .. function:: set([iterable]) |
| :noindex: |
| |
| Return a new :class:`set` object, optionally with elements taken from |
| *iterable*. ``set`` is a built-in class. See :class:`set` and |
| :ref:`types-set` for documentation about this class. |
| |
| For other containers see the built-in :class:`frozenset`, :class:`list`, |
| :class:`tuple`, and :class:`dict` classes, as well as the :mod:`collections` |
| module. |
| |
| .. versionadded:: 2.4 |
| |
| |
| .. function:: setattr(object, name, value) |
| |
| This is the counterpart of :func:`getattr`. The arguments are an object, a |
| string and an arbitrary value. The string may name an existing attribute or a |
| new attribute. The function assigns the value to the attribute, provided the |
| object allows it. For example, ``setattr(x, 'foobar', 123)`` is equivalent to |
| ``x.foobar = 123``. |
| |
| |
| .. function:: slice(stop) |
| 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:`~slice.start`, |
| :attr:`~slice.stop` and :attr:`~slice.step` which merely return the argument |
| values (or their default). They have no other explicit functionality; |
| however they are used by Numerical Python and other third party extensions. |
| Slice objects are also generated when extended indexing syntax is used. For |
| example: ``a[start:stop:step]`` or ``a[start:stop, i]``. See |
| :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 |
| the second argument: ``cmp=lambda x,y: cmp(x.lower(), y.lower())``. The default |
| value is ``None``. |
| |
| *key* specifies a function of one argument that is used to extract a comparison |
| key from each list element: ``key=str.lower``. The default value is ``None`` |
| (compare the elements directly). |
| |
| *reverse* is a boolean value. If set to ``True``, then the list elements are |
| sorted as if each comparison were reversed. |
| |
| In general, the *key* and *reverse* conversion processes are much faster |
| than specifying an equivalent *cmp* function. This is because *cmp* is |
| called multiple times for each list element while *key* and *reverse* touch |
| each element only once. Use :func:`functools.cmp_to_key` to convert an |
| old-style *cmp* function to a *key* function. |
| |
| For sorting examples and a brief sorting tutorial, see `Sorting HowTo |
| <http://wiki.python.org/moin/HowTo/Sorting/>`_\. |
| |
| .. 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(object): |
| @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++. Also see |
| :func:`classmethod` for a variant that is useful for creating alternate |
| class constructors. |
| |
| For more information on static methods, consult the documentation on the |
| standard type hierarchy in :ref:`types`. |
| |
| .. versionadded:: 2.2 |
| |
| .. versionchanged:: 2.4 |
| Function decorator syntax added. |
| |
| |
| .. function:: str(object='') |
| |
| Return a string containing a nicely printable representation of an object. For |
| strings, this returns the string itself. The difference with ``repr(object)`` |
| is that ``str(object)`` does not always attempt to return a string that is |
| acceptable to :func:`eval`; its goal is to return a printable string. If no |
| argument is given, returns the empty string, ``''``. |
| |
| For more information on strings see :ref:`typesseq` which describes sequence |
| functionality (strings are sequences), and also the string-specific methods |
| described in the :ref:`string-methods` section. To output formatted strings |
| use template strings or the ``%`` operator described in the |
| :ref:`string-formatting` section. In addition see the :ref:`stringservices` |
| section. See also :func:`unicode`. |
| |
| |
| .. function:: sum(iterable[, start]) |
| |
| Sums *start* and the items of an *iterable* from left to right and returns the |
| total. *start* defaults to ``0``. The *iterable*'s items are normally numbers, |
| and the start value is not allowed to be a string. |
| |
| For some use cases, there are good alternatives to :func:`sum`. |
| The preferred, fast way to concatenate a sequence of strings is by calling |
| ``''.join(sequence)``. To add floating point values with extended precision, |
| see :func:`math.fsum`\. To concatenate a series of iterables, consider using |
| :func:`itertools.chain`. |
| |
| .. versionadded:: 2.3 |
| |
| |
| .. function:: super(type[, object-or-type]) |
| |
| Return a proxy object that delegates method calls to a parent or sibling |
| class of *type*. This is useful for accessing inherited methods that have |
| been overridden in a class. The search order is same as that used by |
| :func:`getattr` except that the *type* itself is skipped. |
| |
| The :attr:`~class.__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): |
| def method(self, arg): |
| 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 |
| 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 form specifies the arguments exactly and makes the appropriate |
| references. |
| |
| For practical suggestions on how to design cooperative classes using |
| :func:`super`, see `guide to using super() |
| <http://rhettinger.wordpress.com/2011/05/26/super-considered-super/>`_. |
| |
| .. versionadded:: 2.2 |
| |
| |
| .. function:: tuple([iterable]) |
| |
| Return a tuple whose items are the same and in the same order as *iterable*'s |
| items. *iterable* may be a sequence, a container that supports iteration, or an |
| iterator object. If *iterable* is already a tuple, it is returned unchanged. |
| For instance, ``tuple('abc')`` returns ``('a', 'b', 'c')`` and ``tuple([1, 2, |
| 3])`` returns ``(1, 2, 3)``. If no argument is given, returns a new empty |
| tuple, ``()``. |
| |
| :class:`tuple` is an immutable sequence type, as documented in |
| :ref:`typesseq`. For other containers see the built in :class:`dict`, |
| :class:`list`, and :class:`set` classes, and the :mod:`collections` module. |
| |
| |
| .. function:: type(object) |
| type(name, bases, dict) |
| |
| .. index:: object: type |
| |
| With one argument, 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, 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:`~class.__name__` attribute; the *bases* tuple |
| itemizes the base classes and becomes the :attr:`~class.__bases__` attribute; |
| and the *dict* dictionary is the namespace containing definitions for class |
| body and becomes the :attr:`~object.__dict__` attribute. For example, the |
| following two statements create identical :class:`type` objects: |
| |
| >>> class X(object): |
| ... a = 1 |
| ... |
| >>> X = type('X', (object,), dict(a=1)) |
| |
| .. versionadded:: 2.2 |
| |
| |
| .. function:: unichr(i) |
| |
| Return the Unicode string of one character whose Unicode code is the integer |
| *i*. For example, ``unichr(97)`` returns the string ``u'a'``. This is the |
| inverse of :func:`ord` for Unicode strings. The valid range for the argument |
| depends how Python was configured -- it may be either UCS2 [0..0xFFFF] or UCS4 |
| [0..0x10FFFF]. :exc:`ValueError` is raised otherwise. For ASCII and 8-bit |
| strings see :func:`chr`. |
| |
| .. versionadded:: 2.0 |
| |
| |
| .. function:: unicode(object='') |
| unicode(object[, encoding [, errors]]) |
| |
| Return the Unicode string version of *object* using one of the following modes: |
| |
| If *encoding* and/or *errors* are given, ``unicode()`` will decode the object |
| which can either be an 8-bit string or a character buffer using the codec for |
| *encoding*. The *encoding* parameter is a string giving the name of an encoding; |
| if the encoding is not known, :exc:`LookupError` is raised. Error handling is |
| done according to *errors*; this specifies the treatment of characters which are |
| invalid in the input encoding. If *errors* is ``'strict'`` (the default), a |
| :exc:`ValueError` is raised on errors, while a value of ``'ignore'`` causes |
| errors to be silently ignored, and a value of ``'replace'`` causes the official |
| Unicode replacement character, ``U+FFFD``, to be used to replace input |
| characters which cannot be decoded. See also the :mod:`codecs` module. |
| |
| If no optional parameters are given, ``unicode()`` will mimic the behaviour of |
| ``str()`` except that it returns Unicode strings instead of 8-bit strings. More |
| precisely, if *object* is a Unicode string or subclass it will return that |
| Unicode string without any additional decoding applied. |
| |
| For objects which provide a :meth:`__unicode__` method, it will call this method |
| without arguments to create a Unicode string. For all other objects, the 8-bit |
| string version or representation is requested and then converted to a Unicode |
| string using the codec for the default encoding in ``'strict'`` mode. |
| |
| For more information on Unicode strings see :ref:`typesseq` which describes |
| sequence functionality (Unicode strings are sequences), and also the |
| string-specific methods described in the :ref:`string-methods` section. To |
| output formatted strings use template strings or the ``%`` operator described |
| in the :ref:`string-formatting` section. In addition see the |
| :ref:`stringservices` section. See also :func:`str`. |
| |
| .. versionadded:: 2.0 |
| |
| .. versionchanged:: 2.2 |
| Support for :meth:`__unicode__` added. |
| |
| |
| .. function:: vars([object]) |
| |
| Return the :attr:`~object.__dict__` attribute for a module, class, instance, |
| or any other object with a :attr:`__dict__` attribute. |
| |
| Objects such as modules and instances have an updateable :attr:`__dict__` |
| attribute; however, other objects may have write restrictions on their |
| :attr:`__dict__` attributes (for example, new-style classes use a |
| dictproxy to prevent direct dictionary updates). |
| |
| Without an argument, :func:`vars` acts like :func:`locals`. Note, the |
| locals dictionary is only useful for reads since updates to the locals |
| dictionary are ignored. |
| |
| |
| .. function:: xrange(stop) |
| xrange(start, stop[, step]) |
| |
| This function is very similar to :func:`range`, but returns an :ref:`xrange |
| object <typesseq-xrange>` |
| instead of a list. This is an opaque sequence type which yields the same values |
| as the corresponding list, without actually storing them all simultaneously. |
| The advantage of :func:`xrange` over :func:`range` is minimal (since |
| :func:`xrange` still has to create the values when asked for them) except when a |
| very large range is used on a memory-starved machine or when all of the range's |
| elements are never used (such as when the loop is usually terminated with |
| :keyword:`break`). For more information on xrange objects, see |
| :ref:`typesseq-xrange` and :ref:`typesseq`. |
| |
| .. impl-detail:: |
| |
| :func:`xrange` is intended to be simple and fast. Implementations may |
| impose restrictions to achieve this. The C implementation of Python |
| restricts all arguments to native C longs ("short" Python integers), and |
| also requires that the number of elements fit in a native C long. 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+2*(step<0))//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. |
| |
| 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 == list(x2) and y == list(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. |
| |
| |
| .. 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, unlike :func:`importlib.import_module`. |
| |
| This function is invoked by the :keyword:`import` statement. It can be |
| replaced (by importing the :mod:`__builtin__` module and assigning to |
| ``__builtin__.__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, |
| use :func:`importlib.import_module`. |
| |
| |
| .. 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. |
| |
| 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 |
| ``function(*args, **keywords)``. |
| |
| .. deprecated:: 2.3 |
| Use ``function(*args, **keywords)`` instead of |
| ``apply(function, args, keywords)`` (see :ref:`tut-unpacking-arguments`). |
| |
| |
| .. function:: buffer(object[, offset[, size]]) |
| |
| The *object* argument must be an object that supports the buffer call interface |
| (such as strings, arrays, and buffers). A new buffer object will be created |
| which references the *object* argument. The buffer object will be a slice from |
| the beginning of *object* (or from the specified *offset*). The slice will |
| extend to the end of *object* (or will have a length given by the *size* |
| argument). |
| |
| |
| .. function:: coerce(x, y) |
| |
| Return a tuple consisting of the two numeric arguments converted to a common |
| type, using the same rules as used by arithmetic operations. If coercion is not |
| possible, raise :exc:`TypeError`. |
| |
| |
| .. function:: intern(string) |
| |
| Enter *string* in the table of "interned" strings and return the interned string |
| -- which is *string* itself or a copy. Interning strings is useful to gain a |
| little performance on dictionary lookup -- if the keys in a dictionary are |
| interned, and the lookup key is interned, the key comparisons (after hashing) |
| can be done by a pointer compare instead of a string compare. Normally, the |
| names used in Python programs are automatically interned, and the dictionaries |
| used to hold module, class or instance attributes have interned keys. |
| |
| .. versionchanged:: 2.3 |
| Interned strings are not immortal (like they used to be in Python 2.2 and |
| before); you must keep a reference to the return value of :func:`intern` around |
| to benefit from it. |
| |
| .. rubric:: Footnotes |
| |
| .. [#] It is used relatively rarely so does not warrant being made into a statement. |
| |
| .. [#] Specifying a buffer size currently has no effect on systems that don't have |
| :c:func:`setvbuf`. The interface to specify the buffer size is not done using a |
| method that calls :c:func:`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. |
| |