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diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst new file mode 100644 index 0000000..b0a5577c --- /dev/null +++ b/Doc/library/functions.rst @@ -0,0 +1,1138 @@ + +.. _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: ihooks + module: rexec + 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 modules + :mod:`ihooks` and :mod:`rexec`. See also the built-in module :mod:`imp`, which + defines some useful operations out of which you can build your own + :func:`__import__` function. + + For example, the statement ``import spam`` results in the following call: + ``__import__('spam',`` ``globals(),`` ``locals(), [], -1)``; the statement + ``from spam.ham import eggs`` results in ``__import__('spam.ham', globals(), + locals(), ['eggs'], -1)``. Note that even though ``locals()`` and ``['eggs']`` + are passed in as arguments, the :func:`__import__` function does not set the + local variable named ``eggs``; this is done by subsequent code that is generated + for the import statement. (In fact, the standard implementation does not use + its *locals* argument at all, and uses its *globals* only to determine the + package context of the :keyword:`import` statement.) + + When the *name* variable is of the form ``package.module``, normally, the + top-level package (the name up till the first dot) is returned, *not* the + module named by *name*. However, when a non-empty *fromlist* argument is + given, the module named by *name* is returned. This is done for + compatibility with the bytecode generated for the different kinds of import + statement; when using ``import spam.ham.eggs``, the top-level package + :mod:`spam` must be placed in the importing namespace, but when using ``from + spam.ham import eggs``, the ``spam.ham`` subpackage must be used to find the + ``eggs`` variable. As a workaround for this behavior, use :func:`getattr` to + extract the desired components. For example, you could define the following + helper:: + + def my_import(name): + mod = __import__(name) + components = name.split('.') + for comp in components[1:]: + mod = getattr(mod, comp) + return mod + + *level* specifies whether to use absolute or relative imports. The default is + ``-1`` which indicates both absolute and relative imports will be attempted. + ``0`` means only perform absolute imports. Positive values for *level* indicate + the number of parent directories to search relative to the directory of the + module calling :func:`__import__`. + + .. versionchanged:: 2.5 + The level parameter was added. + + .. versionchanged:: 2.5 + Keyword support for parameters was added. + + +.. function:: abs(x) + + Return the absolute value of a number. The argument may be a plain or long + integer or a floating point number. If the argument is a complex number, its + magnitude is returned. + + +.. 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 + + .. versionadded:: 2.5 + + +.. 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 + + .. versionadded:: 2.5 + + +.. 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`). + + .. 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:: 3.0 + + +.. 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:: 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`. + + .. 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 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)``. + + .. versionchanged:: 2.3 + Using :func:`divmod` with complex numbers is deprecated. + + +.. 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 + + .. versionadded:: 2.3 + + +.. function:: eval(expression[, globals[, locals]]) + + The arguments are a string and optional globals and locals. If provided, + *globals* must be a dictionary. If provided, *locals* can be any mapping + object. + + .. versionchanged:: 2.4 + formerly *locals* was required to be a dictionary. + + The *expression* argument is parsed and evaluated as a Python expression + (technically speaking, a condition list) using the *globals* and *locals* + 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 + >>> 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. 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 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``. + + +.. 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:: 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. + + .. versionadded:: 2.4 + + +.. function:: getattr(object, name[, default]) + + Return the value of the named attributed of *object*. *name* must be a string. + If the string is the name of one of the object's attributes, the result is the + 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. + + .. versionadded:: 2.2 + + +.. 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. + + .. 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. + (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. Also return true if *classinfo* + is a type object (new-style class) and *object* is an object of that type or of + a (direct or indirect) subclass thereof. If *object* is not a class instance or + an object of the given type, the function always returns false. If *classinfo* + is neither a class object nor a type object, it may be a tuple of class or type + objects, or may recursively contain other such tuples (other sequence types are + not accepted). If *classinfo* is not a class, type, or tuple of classes, types, + and such tuples, a :exc:`TypeError` exception is raised. + + .. versionchanged:: 2.2 + Support for a tuple of type information was added. + + +.. function:: issubclass(class, classinfo) + + Return true if *class* is a subclass (direct or indirect) of *classinfo*. A + 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 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. + + .. 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. + + .. 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, ...) + + 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[, args...][key]) + + With a single argument *iterable*, return the largest item of a non-empty + iterable (such as a string, tuple or list). With more than one argument, return + the largest of the arguments. + + The optional *key* argument specifies a one-argument ordering function like that + used for :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. + + +.. 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 *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 *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 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 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. + + .. versionchanged:: 2.4 + Formerly only returned an unsigned literal. + + +.. 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. + + .. 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:: property([fget[, fset[, fdel[, doc]]]]) + + Return a property attribute for new-style classes (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 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. + + .. versionadded:: 2.2 + + .. versionchanged:: 2.5 + Use *fget*'s docstring if no *doc* given. + + +.. function:: range([start,] stop[, step]) + + This is a versatile function to create sequences 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:: + + >>> 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``). + + .. versionadded:: 2.4 + + +.. 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. + + .. 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([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. + + .. versionadded:: 2.4 + + +.. function:: staticmethod(function) + + Return a static method for *function*. + + A static method does not receive an implicit first argument. To declare a static + method, use this idiom:: + + class C: + @staticmethod + def f(arg1, arg2, ...): ... + + 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`. + + .. versionadded:: 2.2 + + .. versionchanged:: 2.4 + Function decorator syntax added. + + +.. 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 + 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 are not allowed to be strings. The fast, correct way to concatenate a + sequence of strings is by calling ``''.join(sequence)``. + + .. versionadded:: 2.3 + + +.. function:: super(type[, object-or-type]) + + 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. :func:`super` only works for new-style + classes. + + 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]``. + + .. 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) + + .. index:: object: type + + Return the type of an *object*. The return value is a type object. The + :func:`isinstance` built-in function is recommended for testing the type of an + object. + + With three arguments, :func:`type` functions as a constructor as detailed below. + + +.. function:: type(name, bases, dict) + :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)) + + .. versionadded:: 2.2 + + +.. 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 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. + + .. 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. + +.. % --------------------------------------------------------------------------- + + +.. _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. + + +.. 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. + |