| |
| .. _built-in-funcs: |
| |
| Built-in Functions |
| ================== |
| |
| The Python interpreter has a number of functions built into it that are always |
| available. They are listed here in alphabetical order. |
| |
| |
| .. function:: __import__(name[, globals[, locals[, fromlist[, level]]]]) |
| |
| .. index:: |
| statement: import |
| module: imp |
| |
| .. note:: |
| |
| This is an advanced function that is not needed in everyday Python |
| programming. |
| |
| The function is invoked by the :keyword:`import` statement. It mainly exists |
| so that you can replace it with another function that has a compatible |
| interface, in order to change the semantics of the :keyword:`import` |
| statement. For examples of why and how you would do this, see the standard |
| library module :mod:`ihooks`. 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__`. |
| |
| |
| .. function:: abs(x) |
| |
| Return the absolute value of a number. The argument may be a plain or long |
| integer or a floating point number. If the argument is a complex number, its |
| magnitude is returned. |
| |
| |
| .. function:: all(iterable) |
| |
| Return True if all elements of the *iterable* are true. Equivalent to:: |
| |
| def all(iterable): |
| for element in iterable: |
| if not element: |
| return False |
| return True |
| |
| |
| .. function:: any(iterable) |
| |
| Return True if any element of the *iterable* is true. Equivalent to:: |
| |
| def any(iterable): |
| for element in iterable: |
| if element: |
| return True |
| return False |
| |
| |
| .. function:: basestring() |
| |
| This abstract type is the superclass for :class:`str`. It |
| cannot be called or instantiated, but it can be used to test whether an object |
| is an instance of :class:`str` (or a user-defined type inherited from |
| :class:`basestring`). |
| |
| |
| .. function:: bin(x) |
| |
| Convert an integer number to a binary string. The result is a valid Python |
| expression. If *x* is not a Python :class:`int` object, it has to define an |
| :meth:`__index__` method that returns an integer. |
| |
| |
| .. function:: bool([x]) |
| |
| Convert a value to a Boolean, using the standard truth testing procedure. If |
| *x* is false or omitted, this returns :const:`False`; otherwise it returns |
| :const:`True`. :class:`bool` is also a class, which is a subclass of |
| :class:`int`. Class :class:`bool` cannot be subclassed further. Its only |
| instances are :const:`False` and :const:`True`. |
| |
| .. index:: pair: Boolean; type |
| |
| |
| .. function:: bytes([arg[, encoding[, errors]]]) |
| |
| Return a new array of bytes. The :class:`bytes` 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 a few |
| methods borrowed from strings, described in :ref:`bytes-methods`. |
| |
| The optional *arg* parameter can be used to initialize the array in a few |
| different ways: |
| |
| * If it is a *string*, you must also give the *encoding* (and optionally, |
| *errors*) parameters; :func:`bytes` then acts like :meth:`str.encode`. |
| |
| * If it is an *integer*, the array will have that size and will be |
| initialized with null bytes. |
| |
| * If it is an object conforming to the *buffer* interface, a read-only buffer |
| of the object will be used to initialize the bytes array. |
| |
| * If it is an *iterable*, it must be an iterable of integers in the range 0 |
| <= x < 256, which are used as the initial contents of the array. |
| |
| Without an argument, an array of size 0 is created. |
| |
| |
| .. function:: chr(i) |
| |
| Return the string of one character whose Unicode codepoint is the integer |
| *i*. For example, ``chr(97)`` returns the string ``'a'``. This is the |
| inverse of :func:`ord`. The valid range for the argument depends how Python |
| was configured -- it may be either UCS2 [0..0xFFFF] or UCS4 [0..0x10FFFF]. |
| :exc:`ValueError` will be raised if *i* is outside that range. |
| |
| |
| .. function:: classmethod(function) |
| |
| Return a class method for *function*. |
| |
| A class method receives the class as implicit first argument, just like an |
| instance method receives the instance. To declare a class method, use this |
| idiom:: |
| |
| class C: |
| @classmethod |
| def f(cls, arg1, arg2, ...): ... |
| |
| The ``@classmethod`` form is a function decorator -- see the description of |
| function definitions in :ref:`function` for details. |
| |
| It can be called either on the class (such as ``C.f()``) or on an instance (such |
| as ``C().f()``). The instance is ignored except for its class. If a class |
| method is called for a derived class, the derived class object is passed as the |
| implied first argument. |
| |
| Class methods are different than C++ or Java static methods. If you want those, |
| see :func:`staticmethod` in this section. |
| |
| For more information on class methods, consult the documentation on the standard |
| type hierarchy in :ref:`types`. |
| |
| |
| .. function:: cmp(x, y) |
| |
| Compare the two objects *x* and *y* and return an integer according to the |
| outcome. The return value is negative if ``x < y``, zero if ``x == y`` and |
| strictly positive if ``x > y``. |
| |
| |
| .. function:: compile(source, filename, mode[, flags[, dont_inherit]]) |
| |
| Compile the *source* into a code object. Code objects can be executed by a call |
| to :func:`exec` or evaluated by a call to :func:`eval`. The *filename* argument |
| should give the file from which the code was read; pass some recognizable value |
| if it wasn't read from a file (``'<string>'`` is commonly used). The *mode* |
| argument specifies what kind of code must be compiled; it can be ``'exec'`` if |
| *source* consists of a sequence of statements, ``'eval'`` if it consists of a |
| single expression, or ``'single'`` if it consists of a single interactive |
| statement (in the latter case, expression statements that evaluate to something |
| else than ``None`` will be printed). |
| |
| When compiling multi-line statements, two caveats apply: line endings must be |
| represented by a single newline character (``'\n'``), and the input must be |
| terminated by at least one newline character. If line endings are represented |
| by ``'\r\n'``, use the string :meth:`replace` method to change them into |
| ``'\n'``. |
| |
| The optional arguments *flags* and *dont_inherit* (which are new in Python 2.2) |
| control which future statements (see :pep:`236`) affect the compilation of |
| *source*. If neither is present (or both are zero) the code is compiled with |
| those future statements that are in effect in the code that is calling compile. |
| If the *flags* argument is given and *dont_inherit* is not (or is zero) then the |
| future statements specified by the *flags* argument are used in addition to |
| those that would be used anyway. If *dont_inherit* is a non-zero integer then |
| the *flags* argument is it -- the future statements in effect around the call to |
| compile are ignored. |
| |
| Future statements are specified by bits which can be bitwise or-ed together to |
| specify multiple statements. The bitfield required to specify a given feature |
| can be found as the :attr:`compiler_flag` attribute on the :class:`_Feature` |
| instance in the :mod:`__future__` module. |
| |
| |
| .. function:: complex([real[, imag]]) |
| |
| Create a complex number with the value *real* + *imag*\*j or convert a string or |
| number to a complex number. If the first parameter is a string, it will be |
| interpreted as a complex number and the function must be called without a second |
| parameter. The second parameter can never be a string. Each argument may be any |
| numeric type (including complex). If *imag* is omitted, it defaults to zero and |
| the function serves as a numeric conversion function like :func:`int`, |
| :func:`long` and :func:`float`. If both arguments are omitted, returns ``0j``. |
| |
| The complex type is described in :ref:`typesnumeric`. |
| |
| |
| .. function:: delattr(object, name) |
| |
| This is a relative of :func:`setattr`. The arguments are an object and a |
| string. The string must be the name of one of the object's attributes. The |
| function deletes the named attribute, provided the object allows it. For |
| example, ``delattr(x, 'foobar')`` is equivalent to ``del x.foobar``. |
| |
| |
| .. function:: dict([arg]) |
| :noindex: |
| |
| Create a new data dictionary, optionally with items taken from *arg*. |
| The dictionary type is described in :ref:`typesmapping`. |
| |
| For other containers see the built in :class:`list`, :class:`set`, and |
| :class:`tuple` classes, and the :mod:`collections` module. |
| |
| |
| .. function:: dir([object]) |
| |
| Without arguments, return the list of names in the current local scope. With an |
| argument, attempt to return a list of valid attributes for that object. |
| |
| If the object has a method named :meth:`__dir__`, this method will be called and |
| must return the list of attributes. This allows objects that implement a custom |
| :func:`__getattr__` or :func:`__getattribute__` function to customize the way |
| :func:`dir` reports their attributes. |
| |
| If the object does not provide :meth:`__dir__`, the function tries its best to |
| gather information from the object's :attr:`__dict__` attribute, if defined, and |
| from its type object. The resulting list is not necessarily complete, and may |
| be inaccurate when the object has a custom :func:`__getattr__`. |
| |
| The default :func:`dir` mechanism behaves differently with different types of |
| objects, as it attempts to produce the most relevant, rather than complete, |
| information: |
| |
| * If the object is a module object, the list contains the names of the module's |
| attributes. |
| |
| * If the object is a type or class object, the list contains the names of its |
| attributes, and recursively of the attributes of its bases. |
| |
| * Otherwise, the list contains the object's attributes' names, the names of its |
| class's attributes, and recursively of the attributes of its class's base |
| classes. |
| |
| The resulting list is sorted alphabetically. For example:: |
| |
| >>> import struct |
| >>> dir() |
| ['__builtins__', '__doc__', '__name__', 'struct'] |
| >>> dir(struct) |
| ['__doc__', '__name__', 'calcsize', 'error', 'pack', 'unpack'] |
| >>> class Foo(object): |
| ... def __dir__(self): |
| ... return ["kan", "ga", "roo"] |
| ... |
| >>> f = Foo() |
| >>> dir(f) |
| ['ga', 'kan', 'roo'] |
| |
| .. note:: |
| |
| Because :func:`dir` is supplied primarily as a convenience for use at an |
| interactive prompt, it tries to supply an interesting set of names more than it |
| tries to supply a rigorously or consistently defined set of names, and its |
| detailed behavior may change across releases. |
| |
| |
| .. function:: divmod(a, b) |
| |
| Take two (non complex) numbers as arguments and return a pair of numbers |
| consisting of their quotient and remainder when using long division. With mixed |
| operand types, the rules for binary arithmetic operators apply. For plain and |
| long integers, the result is the same as ``(a // b, a % b)``. For floating point |
| numbers the result is ``(q, a % b)``, where *q* is usually ``math.floor(a / b)`` |
| but may be 1 less than that. In any case ``q * b + a % b`` is very close to |
| *a*, if ``a % b`` is non-zero it has the same sign as *b*, and ``0 <= abs(a % b) |
| < abs(b)``. |
| |
| |
| .. function:: enumerate(iterable) |
| |
| Return an enumerate object. *iterable* must be a sequence, an iterator, or some |
| other object which supports iteration. The :meth:`__next__` method of the |
| iterator returned by :func:`enumerate` returns a tuple containing a count (from |
| zero) and the corresponding value obtained from iterating over *iterable*. |
| :func:`enumerate` is useful for obtaining an indexed series: ``(0, seq[0])``, |
| ``(1, seq[1])``, ``(2, seq[2])``, .... For example:: |
| |
| >>> for i, season in enumerate(['Spring', 'Summer', 'Fall', 'Winter')]: |
| >>> print(i, season) |
| 0 Spring |
| 1 Summer |
| 2 Fall |
| 3 Winter |
| |
| |
| .. function:: eval(expression[, globals[, locals]]) |
| |
| The arguments are a string and optional globals and locals. If provided, |
| *globals* must be a dictionary. If provided, *locals* can be any mapping |
| object. |
| |
| The *expression* argument is parsed and evaluated as a Python expression |
| (technically speaking, a condition list) using the *globals* and *locals* |
| dictionaries as global and local name space. If the *globals* dictionary is |
| present and lacks '__builtins__', the current globals are copied into *globals* |
| before *expression* is parsed. This means that *expression* normally has full |
| access to the standard :mod:`__builtin__` module and restricted environments are |
| propagated. If the *locals* dictionary is omitted it defaults to the *globals* |
| dictionary. If both dictionaries are omitted, the expression is executed in the |
| environment where :keyword:`eval` is called. The return value is the result of |
| the evaluated expression. Syntax errors are reported as exceptions. Example:: |
| |
| >>> x = 1 |
| >>> eval('x+1') |
| 2 |
| |
| This function can also be used to execute arbitrary code objects (such as those |
| created by :func:`compile`). In this case pass a code object instead of a |
| string. The code object must have been compiled passing ``'eval'`` as the |
| *kind* argument. |
| |
| Hints: dynamic execution of statements is supported by the :func:`exec` |
| function. The :func:`globals` and :func:`locals` functions |
| returns the current global and local dictionary, respectively, which may be |
| useful to pass around for use by :func:`eval` or :func:`exec`. |
| |
| |
| .. function:: exec(object[, globals[, locals]]) |
| |
| This function supports dynamic execution of Python code. *object* must be either |
| a string, an open file object, or a code object. If it is a string, the string |
| is parsed as a suite of Python statements which is then executed (unless a |
| syntax error occurs). If it is an open file, the file is parsed until EOF and |
| executed. If it is a code object, it is simply executed. In all cases, the |
| code that's executed is expected to be valid as file input (see the section |
| "File input" in the Reference Manual). Be aware that the :keyword:`return` and |
| :keyword:`yield` statements may not be used outside of function definitions even |
| within the context of code passed to the :func:`exec` function. The return value |
| is ``None``. |
| |
| In all cases, if the optional parts are omitted, the code is executed in the |
| current scope. If only *globals* is provided, it must be a dictionary, which |
| will be used for both the global and the local variables. If *globals* and |
| *locals* are given, they are used for the global and local variables, |
| respectively. If provided, *locals* can be any mapping object. |
| |
| If the *globals* dictionary does not contain a value for the key |
| ``__builtins__``, a reference to the dictionary of the built-in module |
| :mod:`__builtin__` is inserted under that key. That way you can control what |
| builtins are available to the executed code by inserting your own |
| ``__builtins__`` dictionary into *globals* before passing it to :func:`exec`. |
| |
| .. note:: |
| |
| The built-in functions :func:`globals` and :func:`locals` return the current |
| global and local dictionary, respectively, which may be useful to pass around |
| for use as the second and third argument to :func:`exec`. |
| |
| .. warning:: |
| |
| The default *locals* act as described for function :func:`locals` below: |
| modifications to the default *locals* dictionary should not be attempted. Pass |
| an explicit *locals* dictionary if you need to see effects of the code on |
| *locals* after function :func:`execfile` returns. :func:`exec` cannot be |
| used reliably to modify a function's locals. |
| |
| |
| .. function:: filter(function, iterable) |
| |
| Construct an iterator from those elements of *iterable* for which *function* |
| returns true. *iterable* may be either a sequence, a container which |
| supports iteration, or an iterator, If *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 the generator |
| expression ``(item for item in iterable if function(item))`` if function is |
| not ``None`` and ``(item for item in iterable if item)`` if function is |
| ``None``. |
| |
| |
| .. function:: float([x]) |
| |
| Convert a string or a number to floating point. If the argument is a string, it |
| must contain a possibly signed decimal or floating point number, possibly |
| embedded in whitespace. Otherwise, the argument may be a plain or long integer |
| or a floating point number, and a floating point number with the same value |
| (within Python's floating point precision) is returned. If no argument is |
| given, returns ``0.0``. |
| |
| .. note:: |
| |
| .. index:: |
| single: NaN |
| single: Infinity |
| |
| When passing in a string, values for NaN and Infinity may be returned, depending |
| on the underlying C library. The specific set of strings accepted which cause |
| these values to be returned depends entirely on the C library and is known to |
| vary. |
| |
| The float type is described in :ref:`typesnumeric`. |
| |
| .. function:: format(value[, format_spec]) |
| |
| .. index:: |
| pair: str; format |
| single: __format__ |
| |
| Convert a string or a number to a "formatted" representation, as controlled |
| by *format_spec*. The interpretation of *format_spec* will depend on the |
| type of the *value* argument, however there is a standard formatting syntax |
| that is used by most built-in types: :ref:`formatspec`. |
| |
| .. note:: |
| |
| ``format(value, format_spec)`` merely calls ``value.__format__(format_spec)``. |
| |
| |
| .. function:: frozenset([iterable]) |
| :noindex: |
| |
| Return a frozenset object, optionally with elements taken from *iterable*. |
| The frozenset type is described in :ref:`types-set`. |
| |
| For other containers see the built in :class:`dict`, :class:`list`, and |
| :class:`tuple` classes, and the :mod:`collections` module. |
| |
| |
| .. function:: getattr(object, name[, default]) |
| |
| Return the value of the named attributed of *object*. *name* must be a string. |
| If the string is the name of one of the object's attributes, the result is the |
| value of that attribute. For example, ``getattr(x, 'foobar')`` is equivalent to |
| ``x.foobar``. If the named attribute does not exist, *default* is returned if |
| provided, otherwise :exc:`AttributeError` is raised. |
| |
| |
| .. function:: globals() |
| |
| Return a dictionary representing the current global symbol table. This is always |
| the dictionary of the current module (inside a function or method, this is the |
| module where it is defined, not the module from which it is called). |
| |
| |
| .. function:: hasattr(object, name) |
| |
| The arguments are an object and a string. The result is ``True`` if the string |
| is the name of one of the object's attributes, ``False`` if not. (This is |
| implemented by calling ``getattr(object, name)`` and seeing whether it raises an |
| exception or not.) |
| |
| |
| .. function:: hash(object) |
| |
| Return the hash value of the object (if it has one). Hash values are integers. |
| They are used to quickly compare dictionary keys during a dictionary lookup. |
| Numeric values that compare equal have the same hash value (even if they are of |
| different types, as is the case for 1 and 1.0). |
| |
| |
| .. function:: help([object]) |
| |
| Invoke the built-in help system. (This function is intended for interactive |
| use.) If no argument is given, the interactive help system starts on the |
| interpreter console. If the argument is a string, then the string is looked up |
| as the name of a module, function, class, method, keyword, or documentation |
| topic, and a help page is printed on the console. If the argument is any other |
| kind of object, a help page on the object is generated. |
| |
| |
| .. function:: hex(x) |
| |
| Convert an integer number to a hexadecimal string. The result is a valid Python |
| expression. If *x* is not a Python :class:`int` object, it has to define an |
| :meth:`__index__` method that returns an integer. |
| |
| |
| .. function:: id(object) |
| |
| Return the "identity" of an object. This is an integer (or long integer) which |
| is guaranteed to be unique and constant for this object during its lifetime. |
| Two objects with non-overlapping lifetimes may have the same :func:`id` value. |
| (Implementation note: this is the address of the object.) |
| |
| |
| .. function:: int([x[, radix]]) |
| |
| Convert a string or number to an integer. If the argument is a string, it |
| must contain a possibly signed number of arbitrary size, |
| possibly embedded in whitespace. The *radix* parameter gives the base for the |
| conversion and may be any integer in the range [2, 36], or zero. If *radix* is |
| zero, the interpretation is the same as for integer literals. If *radix* is |
| specified and *x* is not a string, :exc:`TypeError` is raised. Otherwise, the |
| argument may be another integer, a floating point number or any other object |
| that has an :meth:`__int__` method. Conversion |
| of floating point numbers to integers truncates (towards zero). If no |
| arguments are given, returns ``0``. |
| |
| The integer type is described in :ref:`typesnumeric`. |
| |
| |
| .. function:: isinstance(object, classinfo) |
| |
| Return true if the *object* argument is an instance of the *classinfo* |
| argument, or of a (direct or indirect) subclass thereof. If *object* is not |
| an object of the given type, the function always returns false. If |
| *classinfo* is not a class (type object), it may be a tuple of type objects, |
| or may recursively contain other such tuples (other sequence types are not |
| accepted). If *classinfo* is not a type or tuple of types and such tuples, |
| a :exc:`TypeError` exception is raised. |
| |
| |
| .. function:: issubclass(class, classinfo) |
| |
| Return true if *class* is a subclass (direct or indirect) of *classinfo*. A |
| class is considered a subclass of itself. *classinfo* may be a tuple of class |
| objects, in which case every entry in *classinfo* will be checked. In any other |
| case, a :exc:`TypeError` exception is raised. |
| |
| |
| .. function:: iter(o[, sentinel]) |
| |
| Return an iterator object. The first argument is interpreted very differently |
| depending on the presence of the second argument. Without a second argument, *o* |
| must be a collection object which supports the iteration protocol (the |
| :meth:`__iter__` method), or it must support the sequence protocol (the |
| :meth:`__getitem__` method with integer arguments starting at ``0``). If it |
| does not support either of those protocols, :exc:`TypeError` is raised. If the |
| second argument, *sentinel*, is given, then *o* must be a callable object. The |
| iterator created in this case will call *o* with no arguments for each call to |
| its :meth:`__next__` method; if the value returned is equal to *sentinel*, |
| :exc:`StopIteration` will be raised, otherwise the value will be returned. |
| |
| |
| .. function:: len(s) |
| |
| Return the length (the number of items) of an object. The argument may be a |
| sequence (string, tuple or list) or a mapping (dictionary). |
| |
| |
| .. function:: list([iterable]) |
| |
| Return a list whose items are the same and in the same order as *iterable*'s |
| items. *iterable* may be either a sequence, a container that supports |
| iteration, or an iterator object. If *iterable* is already a list, a copy is |
| made and returned, similar to ``iterable[:]``. For instance, ``list('abc')`` |
| returns ``['a', 'b', 'c']`` and ``list( (1, 2, 3) )`` returns ``[1, 2, 3]``. If |
| no argument is given, returns a new empty list, ``[]``. |
| |
| :class:`list` is a mutable sequence type, as documented in |
| :ref:`typesseq`. For other containers see the built in :class:`dict`, |
| :class:`set`, and :class:`tuple` classes, and the :mod:`collections` module. |
| |
| |
| .. function:: locals() |
| |
| Update and return a dictionary representing the current local symbol table. |
| |
| .. warning:: |
| |
| The contents of this dictionary should not be modified; changes may not affect |
| the values of local variables used by the interpreter. |
| |
| Free variables are returned by *locals* when it is called in a function block. |
| Modifications of free variables may not affect the values used by the |
| interpreter. Free variables are not returned in class blocks. |
| |
| |
| .. function:: map(function, iterable, ...) |
| |
| Return an iterator that applies *function* to every item of *iterable*, |
| yielding the results. If additional *iterable* arguments are passed, |
| *function* must take that many arguments and is applied to the items from all |
| iterables in parallel. 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. |
| |
| Note that for only one *iterable* argument, ``map(function, iterable)`` is |
| equivalent to the generator expression ``(function(item) for item in |
| iterable)`` if *function* is not ``None``. |
| |
| |
| .. function:: max(iterable[, args...], *[, key]) |
| |
| With a single argument *iterable*, return the largest item of a non-empty |
| iterable (such as a string, tuple or list). With more than one argument, return |
| the largest of the arguments. |
| |
| The optional keyword-only *key* argument specifies a one-argument ordering |
| function like that used for :meth:`list.sort`. |
| |
| |
| .. function:: memoryview(obj) |
| |
| Return a "memory view" object created from the given argument. |
| |
| XXX: To be documented. |
| |
| |
| .. function:: min(iterable[, args...], *[, key]) |
| |
| With a single argument *iterable*, return the smallest item of a non-empty |
| iterable (such as a string, tuple or list). With more than one argument, return |
| the smallest of the arguments. |
| |
| The optional keyword-only *key* argument specifies a one-argument ordering |
| function like that used for :meth:`list.sort`. |
| |
| |
| .. function:: next(iterator[, default]) |
| |
| Retrieve the next item from the *iterable* by calling its :meth:`__next__` |
| method. If *default* is given, it is returned if the iterator is exhausted, |
| otherwise :exc:`StopIteration` is raised. |
| |
| |
| .. function:: object() |
| |
| Return a new featureless object. :class:`object` is a base for all classes. |
| It has the methods that are common to all instances of Python classes. This |
| function does not accept any arguments. |
| |
| .. note:: |
| |
| :class:`object` does *not* have a :attr:`__dict__`, so you can't assign |
| arbitrary attributes to an instance of the :class:`object` class. |
| |
| |
| .. function:: oct(x) |
| |
| Convert an integer number to an octal string. The result is a valid Python |
| expression. If *x* is not a Python :class:`int` object, it has to define an |
| :meth:`__index__` method that returns an integer. |
| |
| |
| .. function:: open(filename[, mode[, bufsize]]) |
| |
| Open a file, returning an object of the :class:`file` type described in |
| section :ref:`bltin-file-objects`. If the file cannot be opened, |
| :exc:`IOError` is raised. When opening a file, it's preferable to use |
| :func:`open` instead of invoking the :class:`file` constructor directly. |
| |
| The first two arguments are the same as for ``stdio``'s :cfunc:`fopen`: |
| *filename* is the file name to be opened, and *mode* is a string indicating how |
| the file is to be opened. |
| |
| The most commonly-used values of *mode* are ``'r'`` for reading, ``'w'`` for |
| writing (truncating the file if it already exists), and ``'a'`` for appending |
| (which on *some* Unix systems means that *all* writes append to the end of the |
| file regardless of the current seek position). If *mode* is omitted, it |
| defaults to ``'r'``. When opening a binary file, you should append ``'b'`` to |
| the *mode* value to open the file in binary mode, which will improve |
| portability. (Appending ``'b'`` is useful even on systems that don't treat |
| binary and text files differently, where it serves as documentation.) See below |
| for more possible values of *mode*. |
| |
| .. index:: |
| single: line-buffered I/O |
| single: unbuffered I/O |
| single: buffer size, I/O |
| single: I/O control; buffering |
| |
| The optional *bufsize* argument specifies the file's desired buffer size: 0 |
| means unbuffered, 1 means line buffered, any other positive value means use a |
| buffer of (approximately) that size. A negative *bufsize* means to use the |
| system default, which is usually line buffered for tty devices and fully |
| buffered for other files. If omitted, the system default is used. [#]_ |
| |
| Modes ``'r+'``, ``'w+'`` and ``'a+'`` open the file for updating (note that |
| ``'w+'`` truncates the file). Append ``'b'`` to the mode to open the file in |
| binary mode, on systems that differentiate between binary and text files; on |
| systems that don't have this distinction, adding the ``'b'`` has no effect. |
| |
| In addition to the standard :cfunc:`fopen` values *mode* may be ``'U'`` or |
| ``'rU'``. Python is usually built with universal newline support; supplying |
| ``'U'`` opens the file as a text file, but lines may be terminated by any of the |
| following: the Unix end-of-line convention ``'\n'``, the Macintosh convention |
| ``'\r'``, or the Windows convention ``'\r\n'``. All of these external |
| representations are seen as ``'\n'`` by the Python program. If Python is built |
| without universal newline support a *mode* with ``'U'`` is the same as normal |
| text mode. Note that file objects so opened also have an attribute called |
| :attr:`newlines` which has a value of ``None`` (if no newlines have yet been |
| seen), ``'\n'``, ``'\r'``, ``'\r\n'``, or a tuple containing all the newline |
| types seen. |
| |
| Python enforces that the mode, after stripping ``'U'``, begins with ``'r'``, |
| ``'w'`` or ``'a'``. |
| |
| See also the :mod:`fileinput` module. |
| |
| |
| .. function:: ord(c) |
| |
| Given a string of length one, return an integer representing the Unicode code |
| point of the character when the argument is a unicode object, or the value of |
| the byte when the argument is an 8-bit string. For example, ``ord('a')`` returns |
| the integer ``97``, ``ord(u'\u2020')`` returns ``8224``. This is the inverse of |
| :func:`chr` for 8-bit strings and of :func:`unichr` for unicode objects. If a |
| unicode argument is given and Python was built with UCS2 Unicode, then the |
| character's code point must be in the range [0..65535] inclusive; otherwise the |
| string length is two, and a :exc:`TypeError` will be raised. |
| |
| |
| .. function:: pow(x, y[, z]) |
| |
| Return *x* to the power *y*; if *z* is present, return *x* to the power *y*, |
| modulo *z* (computed more efficiently than ``pow(x, y) % z``). The two-argument |
| form ``pow(x, y)`` is equivalent to using the power operator: ``x**y``. |
| |
| The arguments must have numeric types. With mixed operand types, the coercion |
| rules for binary arithmetic operators apply. For int and long int operands, the |
| result has the same type as the operands (after coercion) unless the second |
| argument is negative; in that case, all arguments are converted to float and a |
| float result is delivered. For example, ``10**2`` returns ``100``, but |
| ``10**-2`` returns ``0.01``. (This last feature was added in Python 2.2. In |
| Python 2.1 and before, if both arguments were of integer types and the second |
| argument was negative, an exception was raised.) If the second argument is |
| negative, the third argument must be omitted. If *z* is present, *x* and *y* |
| must be of integer types, and *y* must be non-negative. (This restriction was |
| added in Python 2.2. In Python 2.1 and before, floating 3-argument ``pow()`` |
| returned platform-dependent results depending on floating-point rounding |
| accidents.) |
| |
| |
| .. function:: property([fget[, fset[, fdel[, doc]]]]) |
| |
| Return a property attribute. |
| |
| *fget* is a function for getting an attribute value, likewise *fset* is a |
| function for setting, and *fdel* a function for del'ing, an attribute. Typical |
| use is to define a managed attribute x:: |
| |
| class C(object): |
| def __init__(self): self._x = None |
| def getx(self): return self._x |
| def setx(self, value): self._x = value |
| def delx(self): del self._x |
| x = property(getx, setx, delx, "I'm the 'x' property.") |
| |
| If given, *doc* will be the docstring of the property attribute. Otherwise, the |
| property will copy *fget*'s docstring (if it exists). This makes it possible to |
| create read-only properties easily using :func:`property` as a decorator:: |
| |
| class Parrot(object): |
| def __init__(self): |
| self._voltage = 100000 |
| |
| @property |
| def voltage(self): |
| """Get the current voltage.""" |
| return self._voltage |
| |
| turns the :meth:`voltage` method into a "getter" for a read-only attribute with |
| the same name. |
| |
| |
| .. XXX does accept objects with __index__ too |
| .. function:: range([start,] stop[, step]) |
| |
| This is a versatile function to create iterators containing arithmetic |
| progressions. It is most often used in :keyword:`for` loops. The arguments |
| must be integers. If the *step* argument is omitted, it defaults to ``1``. |
| If the *start* argument is omitted, it defaults to ``0``. The full form |
| returns an iterator 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:: |
| |
| >>> list(range(10)) |
| [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] |
| >>> list(range(1, 11)) |
| [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] |
| >>> list(range(0, 30, 5)) |
| [0, 5, 10, 15, 20, 25] |
| >>> list(range(0, 10, 3)) |
| [0, 3, 6, 9] |
| >>> list(range(0, -10, -1)) |
| [0, -1, -2, -3, -4, -5, -6, -7, -8, -9] |
| >>> list(range(0)) |
| [] |
| >>> list(range(1, 0)) |
| [] |
| |
| |
| .. function:: repr(object) |
| |
| Return a string containing a printable representation of an object. This is the |
| same value yielded by conversions (reverse quotes). It is sometimes useful to be |
| able to access this operation as an ordinary function. For many types, this |
| function makes an attempt to return a string that would yield an object with the |
| same value when passed to :func:`eval`. |
| |
| |
| .. function:: reversed(seq) |
| |
| Return a reverse iterator. *seq* must be an object which supports the sequence |
| protocol (the :meth:`__len__` method and the :meth:`__getitem__` method with |
| integer arguments starting at ``0``). |
| |
| |
| .. function:: round(x[, n]) |
| |
| Return the floating point value *x* rounded to *n* digits after the decimal |
| point. If *n* is omitted, it defaults to zero. The result is a floating point |
| number. Values are rounded to the closest multiple of 10 to the power minus |
| *n*; if two multiples are equally close, rounding is done away from 0 (so. for |
| example, ``round(0.5)`` is ``1.0`` and ``round(-0.5)`` is ``-1.0``). |
| |
| |
| .. function:: set([iterable]) |
| :noindex: |
| |
| Return a new set, optionally with elements are taken from *iterable*. |
| The set type is described in :ref:`types-set`. |
| |
| For other containers see the built in :class:`dict`, :class:`list`, and |
| :class:`tuple` classes, and the :mod:`collections` module. |
| |
| |
| .. function:: setattr(object, name, value) |
| |
| This is the counterpart of :func:`getattr`. The arguments are an object, a |
| string and an arbitrary value. The string may name an existing attribute or a |
| new attribute. The function assigns the value to the attribute, provided the |
| object allows it. For example, ``setattr(x, 'foobar', 123)`` is equivalent to |
| ``x.foobar = 123``. |
| |
| |
| .. function:: slice([start,] stop[, step]) |
| |
| .. index:: single: Numerical Python |
| |
| Return a slice object representing the set of indices specified by |
| ``range(start, stop, step)``. The *start* and *step* arguments default to |
| ``None``. Slice objects have read-only data attributes :attr:`start`, |
| :attr:`stop` and :attr:`step` which merely return the argument values (or their |
| default). They have no other explicit functionality; however they are used by |
| Numerical Python and other third party extensions. Slice objects are also |
| generated when extended indexing syntax is used. For example: |
| ``a[start:stop:step]`` or ``a[start:stop, i]``. |
| |
| |
| .. function:: sorted(iterable[, cmp[, key[, reverse]]]) |
| |
| Return a new sorted list from the items in *iterable*. |
| |
| The optional arguments *cmp*, *key*, and *reverse* have the same meaning as |
| those for the :meth:`list.sort` method (described in section |
| :ref:`typesseq-mutable`). |
| |
| *cmp* specifies a custom comparison function of two arguments (iterable |
| elements) which should return a negative, zero or positive number depending on |
| whether the first argument is considered smaller than, equal to, or larger than |
| the second argument: ``cmp=lambda x,y: cmp(x.lower(), y.lower())`` |
| |
| *key* specifies a function of one argument that is used to extract a comparison |
| key from each list element: ``key=str.lower`` |
| |
| *reverse* is a boolean value. If set to ``True``, then the list elements are |
| sorted as if each comparison were reversed. |
| |
| In general, the *key* and *reverse* conversion processes are much faster than |
| specifying an equivalent *cmp* function. This is because *cmp* is called |
| multiple times for each list element while *key* and *reverse* touch each |
| element only once. |
| |
| |
| .. function:: staticmethod(function) |
| |
| Return a static method for *function*. |
| |
| A static method does not receive an implicit first argument. To declare a static |
| method, use this idiom:: |
| |
| class C: |
| @staticmethod |
| def f(arg1, arg2, ...): ... |
| |
| The ``@staticmethod`` form is a function decorator -- see the description of |
| function definitions in :ref:`function` for details. |
| |
| It can be called either on the class (such as ``C.f()``) or on an instance (such |
| as ``C().f()``). The instance is ignored except for its class. |
| |
| Static methods in Python are similar to those found in Java or C++. For a more |
| advanced concept, see :func:`classmethod` in this section. |
| |
| For more information on static methods, consult the documentation on the |
| standard type hierarchy in :ref:`types`. |
| |
| |
| .. function:: str([object[, encoding[, errors]]]) |
| |
| Return a string version of an object, using one of the following modes: |
| |
| If *encoding* and/or *errors* are given, :func:`str` will decode the |
| *object* which can either be a byte string or a character buffer using |
| the codec for *encoding*. The *encoding* parameter is a string giving |
| the name of an encoding; if the encoding is not known, :exc:`LookupError` |
| is raised. Error handling is done according to *errors*; this specifies the |
| treatment of characters which are invalid in the input encoding. If |
| *errors* is ``'strict'`` (the default), a :exc:`ValueError` is raised on |
| errors, while a value of ``'ignore'`` causes errors to be silently ignored, |
| and a value of ``'replace'`` causes the official Unicode replacement character, |
| U+FFFD, to be used to replace input characters which cannot be decoded. |
| See also the :mod:`codecs` module. |
| |
| When only *object* is given, this returns its nicely printable representation. |
| For strings, this is the string itself. The difference with ``repr(object)`` |
| is that ``str(object)`` does not always attempt to return a string that is |
| acceptable to :func:`eval`; its goal is to return a printable string. |
| With no arguments, this returns the empty string. |
| |
| Objects can specify what ``str(object)`` returns by defining a :meth:`__str__` |
| special method. |
| |
| For more information on strings see :ref:`typesseq` which describes sequence |
| functionality (strings are sequences), and also the string-specific methods |
| described in the :ref:`string-methods` section. To output formatted strings, |
| see the :ref:`string-formatting` section. In addition see the |
| :ref:`stringservices` section. |
| |
| |
| .. function:: sum(iterable[, start]) |
| |
| Sums *start* and the items of an *iterable* from left to right and returns the |
| total. *start* defaults to ``0``. The *iterable*'s items are normally numbers, |
| and are not allowed to be strings. The fast, correct way to concatenate a |
| sequence of strings is by calling ``''.join(sequence)``. |
| |
| |
| .. function:: super(type[, object-or-type]) |
| |
| .. XXX need to document PEP "new super" |
| |
| Return the superclass of *type*. If the second argument is omitted the super |
| object returned is unbound. If the second argument is an object, |
| ``isinstance(obj, type)`` must be true. If the second argument is a type, |
| ``issubclass(type2, type)`` must be true. |
| |
| A typical use for calling a cooperative superclass method is:: |
| |
| class C(B): |
| def meth(self, arg): |
| super(C, self).meth(arg) |
| |
| Note that :func:`super` is implemented as part of the binding process for |
| explicit dotted attribute lookups such as ``super(C, self).__getitem__(name)``. |
| Accordingly, :func:`super` is undefined for implicit lookups using statements or |
| operators such as ``super(C, self)[name]``. |
| |
| |
| .. function:: tuple([iterable]) |
| |
| Return a tuple whose items are the same and in the same order as *iterable*'s |
| items. *iterable* may be a sequence, a container that supports iteration, or an |
| iterator object. If *iterable* is already a tuple, it is returned unchanged. |
| For instance, ``tuple('abc')`` returns ``('a', 'b', 'c')`` and ``tuple([1, 2, |
| 3])`` returns ``(1, 2, 3)``. If no argument is given, returns a new empty |
| tuple, ``()``. |
| |
| :class:`tuple` is an immutable sequence type, as documented in |
| :ref:`typesseq`. For other containers see the built in :class:`dict`, |
| :class:`list`, and :class:`set` classes, and the :mod:`collections` module. |
| |
| |
| .. function:: type(object) |
| |
| .. index:: object: type |
| |
| Return the type of an *object*. The return value is a type object and |
| generally the same object as returned by ``object.__class__``. |
| |
| The :func:`isinstance` built-in function is recommended for testing the type |
| of an object, because it takes subclasses into account. |
| |
| With three arguments, :func:`type` functions as a constructor as detailed |
| below. |
| |
| |
| .. function:: type(name, bases, dict) |
| :noindex: |
| |
| Return a new type object. This is essentially a dynamic form of the |
| :keyword:`class` statement. The *name* string is the class name and becomes |
| the :attr:`__name__` attribute; the *bases* tuple itemizes the base classes |
| and becomes the :attr:`__bases__` attribute; and the *dict* dictionary is the |
| namespace containing definitions for class body and becomes the |
| :attr:`__dict__` attribute. For example, the following two statements create |
| identical :class:`type` objects:: |
| |
| >>> class X(object): |
| ... a = 1 |
| ... |
| >>> X = type('X', (object,), dict(a=1)) |
| |
| |
| .. function:: vars([object]) |
| |
| Without arguments, return a dictionary corresponding to the current local symbol |
| table. With a module, class or class instance object as argument (or anything |
| else that has a :attr:`__dict__` attribute), returns a dictionary corresponding |
| to the object's symbol table. The returned dictionary should not be modified: |
| the effects on the corresponding symbol table are undefined. [#]_ |
| |
| |
| .. function:: zip([iterable, ...]) |
| |
| This function returns an iterator of tuples, where the *i*-th tuple contains |
| the *i*-th element from each of the argument sequences or iterables. The |
| iterator stops when the shortest argument sequence is exhausted. 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 an iterator of 1-tuples. With no arguments, it |
| returns an empty iterator. |
| |
| |
| .. % --------------------------------------------------------------------------- |
| |
| |
| .. _non-essential-built-in-funcs: |
| |
| Non-essential Built-in Functions |
| ================================ |
| |
| There are several built-in functions that are no longer essential to learn, know |
| or use in modern Python programming. They have been kept here to maintain |
| backwards compatibility with programs written for older versions of Python. |
| |
| Python programmers, trainers, students and bookwriters should feel free to |
| bypass these functions without concerns about missing something important. |
| |
| |
| .. XXX does this go away? |
| .. 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). |
| |
| |
| |
| .. rubric:: Footnotes |
| |
| .. [#] Specifying a buffer size currently has no effect on systems that don't have |
| :cfunc:`setvbuf`. The interface to specify the buffer size is not done using a |
| method that calls :cfunc:`setvbuf`, because that may dump core when called after |
| any I/O has been performed, and there's no reliable way to determine whether |
| this is the case. |
| |
| .. [#] In the current implementation, local variable bindings cannot normally be |
| affected this way, but variables retrieved from other scopes (such as modules) |
| can be. This may change. |
| |