| .. XXX document all delegations to __special__ methods |
| .. _built-in-funcs: |
| |
| Built-in Functions |
| ================== |
| |
| The Python interpreter has a number of functions and types built into it that |
| are always available. They are listed here in alphabetical order. |
| |
| =================== ================= ================== ================ ==================== |
| .. .. Built-in Functions .. .. |
| =================== ================= ================== ================ ==================== |
| :func:`abs` |func-dict|_ :func:`help` :func:`min` :func:`setattr` |
| :func:`all` :func:`dir` :func:`hex` :func:`next` :func:`slice` |
| :func:`any` :func:`divmod` :func:`id` :func:`object` :func:`sorted` |
| :func:`ascii` :func:`enumerate` :func:`input` :func:`oct` :func:`staticmethod` |
| :func:`bin` :func:`eval` :func:`int` :func:`open` :func:`str` |
| :func:`bool` :func:`exec` :func:`isinstance` :func:`ord` :func:`sum` |
| :func:`bytearray` :func:`filter` :func:`issubclass` :func:`pow` :func:`super` |
| :func:`bytes` :func:`float` :func:`iter` :func:`print` :func:`tuple` |
| :func:`callable` :func:`format` :func:`len` :func:`property` :func:`type` |
| :func:`chr` |func-frozenset|_ :func:`list` :func:`range` :func:`vars` |
| :func:`classmethod` :func:`getattr` :func:`locals` :func:`repr` :func:`zip` |
| :func:`compile` :func:`globals` :func:`map` :func:`reversed` :func:`__import__` |
| :func:`complex` :func:`hasattr` :func:`max` :func:`round` |
| :func:`delattr` :func:`hash` |func-memoryview|_ |func-set|_ |
| =================== ================= ================== ================ ==================== |
| |
| .. using :func:`dict` would create a link to another page, so local targets are |
| used, with replacement texts to make the output in the table consistent |
| |
| .. |func-dict| replace:: ``dict()`` |
| .. |func-frozenset| replace:: ``frozenset()`` |
| .. |func-memoryview| replace:: ``memoryview()`` |
| .. |func-set| replace:: ``set()`` |
| |
| |
| .. function:: abs(x) |
| |
| Return the absolute value of a number. The argument may be an |
| integer or a floating point number. If the argument is a complex number, its |
| magnitude is returned. |
| |
| |
| .. function:: all(iterable) |
| |
| Return True if all elements of the *iterable* are true (or if the iterable |
| is empty). 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. If the iterable |
| is empty, return False. Equivalent to:: |
| |
| def any(iterable): |
| for element in iterable: |
| if element: |
| return True |
| return False |
| |
| |
| .. function:: ascii(object) |
| |
| As :func:`repr`, return a string containing a printable representation of an |
| object, but escape the non-ASCII characters in the string returned by |
| :func:`repr` using ``\x``, ``\u`` or ``\U`` escapes. This generates a string |
| similar to that returned by :func:`repr` in Python 2. |
| |
| |
| .. function:: bin(x) |
| |
| Convert an integer number to a binary string. The result is a valid Python |
| expression. If *x* is not a Python :class:`int` object, it has to define an |
| :meth:`__index__` method that returns an integer. |
| |
| |
| .. function:: bool([x]) |
| |
| Convert a value to a Boolean, using the standard :ref:`truth testing |
| procedure <truth>`. If *x* is false or omitted, this returns ``False``; |
| otherwise it returns ``True``. :class:`bool` is also a class, which is a |
| subclass of :class:`int` (see :ref:`typesnumeric`). Class :class:`bool` |
| cannot be subclassed further. Its only instances are ``False`` and |
| ``True`` (see :ref:`bltin-boolean-values`). |
| |
| .. index:: pair: Boolean; type |
| |
| |
| .. function:: bytearray([source[, encoding[, errors]]]) |
| |
| Return a new array of bytes. The :class:`bytearray` type is a mutable |
| sequence of integers in the range 0 <= x < 256. It has most of the usual |
| methods of mutable sequences, described in :ref:`typesseq-mutable`, as well |
| as most methods that the :class:`bytes` type has, see :ref:`bytes-methods`. |
| |
| The optional *source* parameter can be used to initialize the array in a few |
| different ways: |
| |
| * If it is a *string*, you must also give the *encoding* (and optionally, |
| *errors*) parameters; :func:`bytearray` then converts the string to |
| bytes using :meth:`str.encode`. |
| |
| * If it is an *integer*, the array will have that size and will be |
| initialized with null bytes. |
| |
| * If it is an object conforming to the *buffer* interface, a read-only buffer |
| of the object will be used to initialize the bytes array. |
| |
| * If it is an *iterable*, it must be an iterable of integers in the range |
| ``0 <= x < 256``, which are used as the initial contents of the array. |
| |
| Without an argument, an array of size 0 is created. |
| |
| |
| .. function:: bytes([source[, encoding[, errors]]]) |
| |
| Return a new "bytes" object, which is an immutable sequence of integers in |
| the range ``0 <= x < 256``. :class:`bytes` is an immutable version of |
| :class:`bytearray` -- it has the same non-mutating methods and the same |
| indexing and slicing behavior. |
| |
| Accordingly, constructor arguments are interpreted as for :func:`bytearray`. |
| |
| Bytes objects can also be created with literals, see :ref:`strings`. |
| |
| |
| .. function:: callable(object) |
| |
| Return :const:`True` if the *object* argument appears callable, |
| :const:`False` if not. If this returns true, it is still possible that a |
| call fails, but if it is false, calling *object* will never succeed. |
| Note that classes are callable (calling a class returns a new instance); |
| instances are callable if their class has a :meth:`__call__` method. |
| |
| .. versionadded:: 3.2 |
| This function was first removed in Python 3.0 and then brought back |
| in Python 3.2. |
| |
| |
| .. function:: chr(i) |
| |
| Return the string representing a 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 is from 0 through |
| 1,114,111 (0x10FFFF in base 16). :exc:`ValueError` will be raised if *i* is |
| outside that range. |
| |
| |
| .. function:: classmethod(function) |
| |
| Return a class method for *function*. |
| |
| A class method receives the class as implicit first argument, just like an |
| instance method receives the instance. To declare a class method, use this |
| idiom:: |
| |
| class C: |
| @classmethod |
| def f(cls, arg1, arg2, ...): ... |
| |
| The ``@classmethod`` form is a function :term:`decorator` -- see the description |
| of function definitions in :ref:`function` for details. |
| |
| It can be called either on the class (such as ``C.f()``) or on an instance (such |
| as ``C().f()``). The instance is ignored except for its class. If a class |
| method is called for a derived class, the derived class object is passed as the |
| implied first argument. |
| |
| Class methods are different than C++ or Java static methods. If you want those, |
| see :func:`staticmethod` in this section. |
| |
| For more information on class methods, consult the documentation on the standard |
| type hierarchy in :ref:`types`. |
| |
| |
| .. function:: compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1) |
| |
| Compile the *source* into a code or AST object. Code objects can be executed |
| by :func:`exec` or :func:`eval`. *source* can either be a string or an AST |
| object. Refer to the :mod:`ast` module documentation for information on how |
| to work with AST objects. |
| |
| The *filename* argument should give the file from which the code was read; |
| pass some recognizable value if it wasn't read from a file (``'<string>'`` is |
| commonly used). |
| |
| The *mode* argument specifies what kind of code must be compiled; it can be |
| ``'exec'`` if *source* consists of a sequence of statements, ``'eval'`` if it |
| consists of a single expression, or ``'single'`` if it consists of a single |
| interactive statement (in the latter case, expression statements that |
| evaluate to something other than ``None`` will be printed). |
| |
| The optional arguments *flags* and *dont_inherit* control which future |
| statements (see :pep:`236`) affect the compilation of *source*. If neither |
| is present (or both are zero) the code is compiled with those future |
| statements that are in effect in the code that is calling compile. If the |
| *flags* argument is given and *dont_inherit* is not (or is zero) then the |
| future statements specified by the *flags* argument are used in addition to |
| those that would be used anyway. If *dont_inherit* is a non-zero integer then |
| the *flags* argument is it -- the future statements in effect around the call |
| to compile are ignored. |
| |
| Future statements are specified by bits which can be bitwise ORed together to |
| specify multiple statements. The bitfield required to specify a given feature |
| can be found as the :attr:`compiler_flag` attribute on the :class:`_Feature` |
| instance in the :mod:`__future__` module. |
| |
| The argument *optimize* specifies the optimization level of the compiler; the |
| default value of ``-1`` selects the optimization level of the interpreter as |
| given by :option:`-O` options. Explicit levels are ``0`` (no optimization; |
| ``__debug__`` is true), ``1`` (asserts are removed, ``__debug__`` is false) |
| or ``2`` (docstrings are removed too). |
| |
| This function raises :exc:`SyntaxError` if the compiled source is invalid, |
| and :exc:`TypeError` if the source contains null bytes. |
| |
| .. note:: |
| |
| When compiling a string with multi-line code in ``'single'`` or |
| ``'eval'`` mode, input must be terminated by at least one newline |
| character. This is to facilitate detection of incomplete and complete |
| statements in the :mod:`code` module. |
| |
| .. versionchanged:: 3.2 |
| Allowed use of Windows and Mac newlines. Also input in ``'exec'`` mode |
| does not have to end in a newline anymore. Added the *optimize* parameter. |
| |
| |
| .. function:: complex([real[, imag]]) |
| |
| Create a complex number with the value *real* + *imag*\*j or convert a string or |
| number to a complex number. If the first parameter is a string, it will be |
| interpreted as a complex number and the function must be called without a second |
| parameter. The second parameter can never be a string. Each argument may be any |
| numeric type (including complex). If *imag* is omitted, it defaults to zero and |
| the function serves as a numeric conversion function like :func:`int` |
| and :func:`float`. If both arguments are omitted, returns ``0j``. |
| |
| .. note:: |
| |
| When converting from a string, the string must not contain whitespace |
| around the central ``+`` or ``-`` operator. For example, |
| ``complex('1+2j')`` is fine, but ``complex('1 + 2j')`` raises |
| :exc:`ValueError`. |
| |
| The complex type is described in :ref:`typesnumeric`. |
| |
| |
| .. function:: delattr(object, name) |
| |
| This is a relative of :func:`setattr`. The arguments are an object and a |
| string. The string must be the name of one of the object's attributes. The |
| function deletes the named attribute, provided the object allows it. For |
| example, ``delattr(x, 'foobar')`` is equivalent to ``del x.foobar``. |
| |
| |
| .. _func-dict: |
| .. function:: dict([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() # show the names in the module namespace |
| ['__builtins__', '__doc__', '__name__', 'struct'] |
| >>> dir(struct) # show the names in the struct module |
| ['Struct', '__builtins__', '__doc__', '__file__', '__name__', |
| '__package__', '_clearcache', 'calcsize', 'error', 'pack', 'pack_into', |
| 'unpack', 'unpack_from'] |
| >>> class Shape(object): |
| def __dir__(self): |
| return ['area', 'perimeter', 'location'] |
| >>> s = Shape() |
| >>> dir(s) |
| ['area', 'perimeter', 'location'] |
| |
| .. note:: |
| |
| Because :func:`dir` is supplied primarily as a convenience for use at an |
| interactive prompt, it tries to supply an interesting set of names more |
| than it tries to supply a rigorously or consistently defined set of names, |
| and its detailed behavior may change across releases. For example, |
| metaclass attributes are not in the result list when the argument is a |
| class. |
| |
| |
| .. function:: divmod(a, b) |
| |
| Take two (non complex) numbers as arguments and return a pair of numbers |
| consisting of their quotient and remainder when using integer division. With |
| mixed operand types, the rules for binary arithmetic operators apply. For |
| integers, the result is the same as ``(a // b, a % b)``. For floating point |
| numbers the result is ``(q, a % b)``, where *q* is usually ``math.floor(a / |
| b)`` but may be 1 less than that. In any case ``q * b + a % b`` is very |
| close to *a*, if ``a % b`` is non-zero it has the same sign as *b*, and ``0 |
| <= abs(a % b) < abs(b)``. |
| |
| |
| .. function:: enumerate(iterable, start=0) |
| |
| Return an enumerate object. *iterable* must be a sequence, an |
| :term:`iterator`, or some other object which supports iteration. The |
| :meth:`__next__` method of the iterator returned by :func:`enumerate` returns a |
| tuple containing a count (from *start* which defaults to 0) and the |
| values obtained from iterating over *iterable*. |
| |
| >>> seasons = ['Spring', 'Summer', 'Fall', 'Winter'] |
| >>> list(enumerate(seasons)) |
| [(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')] |
| >>> list(enumerate(seasons, start=1)) |
| [(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')] |
| |
| Equivalent to:: |
| |
| def enumerate(sequence, start=0): |
| n = start |
| for elem in sequence: |
| yield n, elem |
| n += 1 |
| |
| |
| .. function:: eval(expression, globals=None, locals=None) |
| |
| The arguments are a string and optional globals and locals. If provided, |
| *globals* must be a dictionary. If provided, *locals* can be any mapping |
| object. |
| |
| The *expression* argument is parsed and evaluated as a Python expression |
| (technically speaking, a condition list) using the *globals* and *locals* |
| dictionaries as global and local namespace. If the *globals* dictionary is |
| present and lacks '__builtins__', the current globals are copied into *globals* |
| before *expression* is parsed. This means that *expression* normally has full |
| access to the standard :mod:`builtins` module and restricted environments are |
| propagated. If the *locals* dictionary is omitted it defaults to the *globals* |
| dictionary. If both dictionaries are omitted, the expression is executed in the |
| environment where :func:`eval` is called. The return value is the result of |
| the evaluated expression. Syntax errors are reported as exceptions. Example: |
| |
| >>> x = 1 |
| >>> eval('x+1') |
| 2 |
| |
| This function can also be used to execute arbitrary code objects (such as |
| those created by :func:`compile`). In this case pass a code object instead |
| of a string. If the code object has been compiled with ``'exec'`` as the |
| *mode* argument, :func:`eval`\'s return value will be ``None``. |
| |
| Hints: dynamic execution of statements is supported by the :func:`exec` |
| function. The :func:`globals` and :func:`locals` functions |
| returns the current global and local dictionary, respectively, which may be |
| useful to pass around for use by :func:`eval` or :func:`exec`. |
| |
| See :func:`ast.literal_eval` for a function that can safely evaluate strings |
| with expressions containing only literals. |
| |
| |
| .. function:: exec(object[, globals[, locals]]) |
| |
| This function supports dynamic execution of Python code. *object* must be |
| either a string or a code object. If it is a string, the string is parsed as |
| a suite of Python statements which is then executed (unless a syntax error |
| occurs). [#]_ If it is a code object, it is simply executed. In all cases, |
| the code that's executed is expected to be valid as file input (see the |
| section "File input" in the Reference Manual). Be aware that the |
| :keyword:`return` and :keyword:`yield` statements may not be used outside of |
| function definitions even within the context of code passed to the |
| :func:`exec` function. The return value is ``None``. |
| |
| In all cases, if the optional parts are omitted, the code is executed in the |
| current scope. If only *globals* is provided, it must be a dictionary, which |
| will be used for both the global and the local variables. If *globals* and |
| *locals* are given, they are used for the global and local variables, |
| respectively. If provided, *locals* can be any mapping object. |
| |
| If the *globals* dictionary does not contain a value for the key |
| ``__builtins__``, a reference to the dictionary of the built-in module |
| :mod:`builtins` is inserted under that key. That way you can control what |
| builtins are available to the executed code by inserting your own |
| ``__builtins__`` dictionary into *globals* before passing it to :func:`exec`. |
| |
| .. note:: |
| |
| The built-in functions :func:`globals` and :func:`locals` return the current |
| global and local dictionary, respectively, which may be useful to pass around |
| for use as the second and third argument to :func:`exec`. |
| |
| .. note:: |
| |
| The default *locals* act as described for function :func:`locals` below: |
| modifications to the default *locals* dictionary should not be attempted. |
| Pass an explicit *locals* dictionary if you need to see effects of the |
| code on *locals* after function :func:`exec` returns. |
| |
| |
| .. function:: filter(function, iterable) |
| |
| Construct an iterator from those elements of *iterable* for which *function* |
| returns true. *iterable* may be either a sequence, a container which |
| supports iteration, or an iterator. If *function* is ``None``, the identity |
| function is assumed, that is, all elements of *iterable* that are false are |
| removed. |
| |
| Note that ``filter(function, iterable)`` is equivalent to the generator |
| expression ``(item for item in iterable if function(item))`` if function is |
| not ``None`` and ``(item for item in iterable if item)`` if function is |
| ``None``. |
| |
| See :func:`itertools.filterfalse` for the complementary function that returns |
| elements of *iterable* for which *function* returns false. |
| |
| |
| .. function:: float([x]) |
| |
| .. index:: |
| single: NaN |
| single: Infinity |
| |
| Convert a string or a number to floating point. |
| |
| If the argument is a string, it should contain a decimal number, optionally |
| preceded by a sign, and optionally embedded in whitespace. The optional |
| sign may be ``'+'`` or ``'-'``; a ``'+'`` sign has no effect on the value |
| produced. The argument may also be a string representing a NaN |
| (not-a-number), or a positive or negative infinity. More precisely, the |
| input must conform to the following grammar after leading and trailing |
| whitespace characters are removed: |
| |
| .. productionlist:: |
| sign: "+" | "-" |
| infinity: "Infinity" | "inf" |
| nan: "nan" |
| numeric_value: `floatnumber` | `infinity` | `nan` |
| numeric_string: [`sign`] `numeric_value` |
| |
| Here ``floatnumber`` is the form of a Python floating-point literal, |
| described in :ref:`floating`. Case is not significant, so, for example, |
| "inf", "Inf", "INFINITY" and "iNfINity" are all acceptable spellings for |
| positive infinity. |
| |
| Otherwise, if the argument is an integer or a floating point number, a |
| floating point number with the same value (within Python's floating point |
| precision) is returned. If the argument is outside the range of a Python |
| float, an :exc:`OverflowError` will be raised. |
| |
| For a general Python object ``x``, ``float(x)`` delegates to |
| ``x.__float__()``. |
| |
| If no argument is given, ``0.0`` is returned. |
| |
| Examples:: |
| |
| >>> float('+1.23') |
| 1.23 |
| >>> float(' -12345\n') |
| -12345.0 |
| >>> float('1e-003') |
| 0.001 |
| >>> float('+1E6') |
| 1000000.0 |
| >>> float('-Infinity') |
| -inf |
| |
| The float type is described in :ref:`typesnumeric`. |
| |
| |
| .. function:: format(value[, format_spec]) |
| |
| .. index:: |
| pair: str; format |
| single: __format__ |
| |
| Convert a *value* to a "formatted" representation, as controlled by |
| *format_spec*. The interpretation of *format_spec* will depend on the type |
| of the *value* argument, however there is a standard formatting syntax that |
| is used by most built-in types: :ref:`formatspec`. |
| |
| The default *format_spec* is an empty string which usually gives the same |
| effect as calling ``str(value)``. |
| |
| A call to ``format(value, format_spec)`` is translated to |
| ``type(value).__format__(format_spec)`` which bypasses the instance |
| dictionary when searching for the value's :meth:`__format__` method. A |
| :exc:`TypeError` exception is raised if the method is not found or if either |
| the *format_spec* or the return value are not strings. |
| |
| |
| .. _func-frozenset: |
| .. 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 attribute of *object*. *name* must be a string. |
| If the string is the name of one of the object's attributes, the result is the |
| value of that attribute. For example, ``getattr(x, 'foobar')`` is equivalent to |
| ``x.foobar``. If the named attribute does not exist, *default* is returned if |
| provided, otherwise :exc:`AttributeError` is raised. |
| |
| |
| .. function:: globals() |
| |
| Return a dictionary representing the current global symbol table. This is always |
| the dictionary of the current module (inside a function or method, this is the |
| module where it is defined, not the module from which it is called). |
| |
| |
| .. function:: hasattr(object, name) |
| |
| The arguments are an object and a string. The result is ``True`` if the |
| string is the name of one of the object's attributes, ``False`` if not. (This |
| is implemented by calling ``getattr(object, name)`` and seeing whether it |
| raises an :exc:`AttributeError` or not.) |
| |
| |
| .. function:: hash(object) |
| |
| Return the hash value of the object (if it has one). Hash values are integers. |
| They are used to quickly compare dictionary keys during a dictionary lookup. |
| Numeric values that compare equal have the same hash value (even if they are of |
| different types, as is the case for 1 and 1.0). |
| |
| |
| .. function:: help([object]) |
| |
| Invoke the built-in help system. (This function is intended for interactive |
| use.) If no argument is given, the interactive help system starts on the |
| interpreter console. If the argument is a string, then the string is looked up |
| as the name of a module, function, class, method, keyword, or documentation |
| topic, and a help page is printed on the console. If the argument is any other |
| kind of object, a help page on the object is generated. |
| |
| This function is added to the built-in namespace by the :mod:`site` module. |
| |
| |
| .. function:: hex(x) |
| |
| Convert an integer number to a hexadecimal string. The result is a valid Python |
| expression. If *x* is not a Python :class:`int` object, it has to define an |
| :meth:`__index__` method that returns an integer. |
| |
| .. note:: |
| |
| To obtain a hexadecimal string representation for a float, use the |
| :meth:`float.hex` method. |
| |
| |
| .. function:: id(object) |
| |
| Return the "identity" of an object. This is an integer which |
| is guaranteed to be unique and constant for this object during its lifetime. |
| Two objects with non-overlapping lifetimes may have the same :func:`id` |
| value. |
| |
| .. impl-detail:: This is the address of the object in memory. |
| |
| |
| .. function:: input([prompt]) |
| |
| If the *prompt* argument is present, it is written to standard output without |
| a trailing newline. The function then reads a line from input, converts it |
| to a string (stripping a trailing newline), and returns that. When EOF is |
| read, :exc:`EOFError` is raised. Example:: |
| |
| >>> s = input('--> ') |
| --> Monty Python's Flying Circus |
| >>> s |
| "Monty Python's Flying Circus" |
| |
| If the :mod:`readline` module was loaded, then :func:`input` will use it |
| to provide elaborate line editing and history features. |
| |
| |
| .. function:: int([number | string[, base]]) |
| |
| Convert a number or string to an integer. If no arguments are given, return |
| ``0``. If a number is given, return ``number.__int__()``. Conversion of |
| floating point numbers to integers truncates towards zero. A string must be |
| a base-radix integer literal optionally preceded by '+' or '-' (with no space |
| in between) and optionally surrounded by whitespace. A base-n literal |
| consists of the digits 0 to n-1, with 'a' to 'z' (or 'A' to 'Z') having |
| values 10 to 35. The default *base* is 10. The allowed values are 0 and 2-36. |
| Base-2, -8, and -16 literals can be optionally prefixed with ``0b``/``0B``, |
| ``0o``/``0O``, or ``0x``/``0X``, as with integer literals in code. Base 0 |
| means to interpret exactly as a code literal, so that the actual base is 2, |
| 8, 10, or 16, and so that ``int('010', 0)`` is not legal, while |
| ``int('010')`` is, as well as ``int('010', 8)``. |
| |
| The integer type is described in :ref:`typesnumeric`. |
| |
| |
| .. function:: isinstance(object, classinfo) |
| |
| Return true if the *object* argument is an instance of the *classinfo* |
| argument, or of a (direct, indirect or :term:`virtual <abstract base |
| class>`) 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, indirect or :term:`virtual |
| <abstract base class>`) of *classinfo*. A |
| class is considered a subclass of itself. *classinfo* may be a tuple of class |
| objects, in which case every entry in *classinfo* will be checked. In any other |
| case, a :exc:`TypeError` exception is raised. |
| |
| |
| .. function:: iter(object[, sentinel]) |
| |
| Return an :term:`iterator` object. The first argument is interpreted very |
| differently depending on the presence of the second argument. Without a |
| second argument, *object* 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 *object* must be a callable object. The iterator created in this case |
| will call *object* 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. |
| |
| One useful application of the second form of :func:`iter` is to read lines of |
| a file until a certain line is reached. The following example reads a file |
| until the :meth:`readline` method returns an empty string:: |
| |
| with open('mydata.txt') as fp: |
| for line in iter(fp.readline, ''): |
| process_line(line) |
| |
| |
| .. function:: len(s) |
| |
| Return the length (the number of items) of an object. The argument may be a |
| sequence (string, tuple or list) or a mapping (dictionary). |
| |
| |
| .. function:: list([iterable]) |
| |
| Return a list whose items are the same and in the same order as *iterable*'s |
| items. *iterable* may be either a sequence, a container that supports |
| iteration, or an iterator object. If *iterable* is already a list, a copy is |
| made and returned, similar to ``iterable[:]``. For instance, ``list('abc')`` |
| returns ``['a', 'b', 'c']`` and ``list( (1, 2, 3) )`` returns ``[1, 2, 3]``. |
| If no argument is given, returns a new empty list, ``[]``. |
| |
| :class:`list` is a mutable sequence type, as documented in :ref:`typesseq`. |
| |
| |
| .. function:: locals() |
| |
| Update and return a dictionary representing the current local symbol table. |
| Free variables are returned by :func:`locals` when it is called in function |
| blocks, but not in class blocks. |
| |
| .. note:: |
| The contents of this dictionary should not be modified; changes may not |
| affect the values of local and free variables used by the interpreter. |
| |
| .. function:: map(function, iterable, ...) |
| |
| Return an iterator that applies *function* to every item of *iterable*, |
| yielding the results. If additional *iterable* arguments are passed, |
| *function* must take that many arguments and is applied to the items from all |
| iterables in parallel. With multiple iterables, the iterator stops when the |
| shortest iterable is exhausted. For cases where the function inputs are |
| already arranged into argument tuples, see :func:`itertools.starmap`\. |
| |
| |
| .. 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`. |
| |
| If multiple items are maximal, the function returns the first one |
| encountered. This is consistent with other sort-stability preserving tools |
| such as ``sorted(iterable, key=keyfunc, reverse=True)[0]`` and |
| ``heapq.nlargest(1, iterable, key=keyfunc)``. |
| |
| |
| .. _func-memoryview: |
| .. function:: memoryview(obj) |
| :noindex: |
| |
| Return a "memory view" object created from the given argument. See |
| :ref:`typememoryview` for more information. |
| |
| |
| .. function:: min(iterable[, 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`. |
| |
| If multiple items are minimal, the function returns the first one |
| encountered. This is consistent with other sort-stability preserving tools |
| such as ``sorted(iterable, key=keyfunc)[0]`` and ``heapq.nsmallest(1, |
| iterable, key=keyfunc)``. |
| |
| .. function:: next(iterator[, default]) |
| |
| Retrieve the next item from the *iterator* by calling its :meth:`__next__` |
| method. If *default* is given, it is returned if the iterator is exhausted, |
| otherwise :exc:`StopIteration` is raised. |
| |
| |
| .. function:: object() |
| |
| Return a new featureless object. :class:`object` is a base for all classes. |
| It has the methods that are common to all instances of Python classes. This |
| function does not accept any arguments. |
| |
| .. note:: |
| |
| :class:`object` does *not* have a :attr:`__dict__`, so you can't assign |
| arbitrary attributes to an instance of the :class:`object` class. |
| |
| |
| .. function:: oct(x) |
| |
| Convert an integer number to an octal string. The result is a valid Python |
| expression. If *x* is not a Python :class:`int` object, it has to define an |
| :meth:`__index__` method that returns an integer. |
| |
| |
| .. function:: open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None) |
| |
| Open *file* and return a corresponding stream. If the file cannot be opened, |
| an :exc:`OSError` is raised. |
| |
| *file* is either a string or bytes object giving the pathname (absolute or |
| relative to the current working directory) of the file to be opened or |
| an integer file descriptor of the file to be wrapped. (If a file descriptor |
| is given, it is closed when the returned I/O object is closed, unless |
| *closefd* is set to ``False``.) |
| |
| *mode* is an optional string that specifies the mode in which the file is |
| opened. It defaults to ``'r'`` which means open for reading in text mode. |
| Other common values are ``'w'`` for writing (truncating the file if it |
| already exists), and ``'a'`` for appending (which on *some* Unix systems, |
| means that *all* writes append to the end of the file regardless of the |
| current seek position). In text mode, if *encoding* is not specified the |
| encoding used is platform dependent. (For reading and writing raw bytes use |
| binary mode and leave *encoding* unspecified.) The available modes are: |
| |
| ========= =============================================================== |
| Character Meaning |
| --------- --------------------------------------------------------------- |
| ``'r'`` open for reading (default) |
| ``'w'`` open for writing, truncating the file first |
| ``'a'`` open for writing, appending to the end of the file if it exists |
| ``'b'`` binary mode |
| ``'t'`` text mode (default) |
| ``'+'`` open a disk file for updating (reading and writing) |
| ``'U'`` universal newline mode (for backwards compatibility; should |
| not be used in new code) |
| ========= =============================================================== |
| |
| The default mode is ``'r'`` (open for reading text, synonym of ``'rt'``). |
| For binary read-write access, the mode ``'w+b'`` opens and truncates the file |
| to 0 bytes. ``'r+b'`` opens the file without truncation. |
| |
| As mentioned in the :ref:`io-overview`, Python distinguishes between binary |
| and text I/O. Files opened in binary mode (including ``'b'`` in the *mode* |
| argument) return contents as :class:`bytes` objects without any decoding. In |
| text mode (the default, or when ``'t'`` is included in the *mode* argument), |
| the contents of the file are returned as :class:`str`, the bytes having been |
| first decoded using a platform-dependent encoding or using the specified |
| *encoding* if given. |
| |
| .. note:: |
| |
| Python doesn't depend on the underlying operating system's notion of text |
| files; all the processing is done by Python itself, and is therefore |
| platform-independent. |
| |
| *buffering* is an optional integer used to set the buffering policy. Pass 0 |
| to switch buffering off (only allowed in binary mode), 1 to select line |
| buffering (only usable in text mode), and an integer > 1 to indicate the size |
| of a fixed-size chunk buffer. When no *buffering* argument is given, the |
| default buffering policy works as follows: |
| |
| * Binary files are buffered in fixed-size chunks; the size of the buffer is |
| chosen using a heuristic trying to determine the underlying device's "block |
| size" and falling back on :attr:`io.DEFAULT_BUFFER_SIZE`. On many systems, |
| the buffer will typically be 4096 or 8192 bytes long. |
| |
| * "Interactive" text files (files for which :meth:`isatty` returns True) use |
| line buffering. Other text files use the policy described above for binary |
| files. |
| |
| *encoding* is the name of the encoding used to decode or encode the file. |
| This should only be used in text mode. The default encoding is platform |
| dependent (whatever :func:`locale.getpreferredencoding` returns), but any |
| encoding supported by Python can be used. See the :mod:`codecs` module for |
| the list of supported encodings. |
| |
| *errors* is an optional string that specifies how encoding and decoding |
| errors are to be handled--this cannot be used in binary mode. Pass |
| ``'strict'`` to raise a :exc:`ValueError` exception if there is an encoding |
| error (the default of ``None`` has the same effect), or pass ``'ignore'`` to |
| ignore errors. (Note that ignoring encoding errors can lead to data loss.) |
| ``'replace'`` causes a replacement marker (such as ``'?'``) to be inserted |
| where there is malformed data. When writing, ``'xmlcharrefreplace'`` |
| (replace with the appropriate XML character reference) or |
| ``'backslashreplace'`` (replace with backslashed escape sequences) can be |
| used. Any other error handling name that has been registered with |
| :func:`codecs.register_error` is also valid. |
| |
| *newline* controls how universal newlines works (it only applies to text |
| mode). It can be ``None``, ``''``, ``'\n'``, ``'\r'``, and ``'\r\n'``. It |
| works as follows: |
| |
| * On input, if *newline* is ``None``, universal newlines mode is enabled. |
| Lines in the input can end in ``'\n'``, ``'\r'``, or ``'\r\n'``, and these |
| are translated into ``'\n'`` before being returned to the caller. If it is |
| ``''``, universal newline mode is enabled, but line endings are returned to |
| the caller untranslated. If it has any of the other legal values, input |
| lines are only terminated by the given string, and the line ending is |
| returned to the caller untranslated. |
| |
| * On output, if *newline* is ``None``, any ``'\n'`` characters written are |
| translated to the system default line separator, :data:`os.linesep`. If |
| *newline* is ``''``, no translation takes place. If *newline* is any of |
| the other legal values, any ``'\n'`` characters written are translated to |
| the given string. |
| |
| If *closefd* is ``False`` and a file descriptor rather than a filename was |
| given, the underlying file descriptor will be kept open when the file is |
| closed. If a filename is given *closefd* has no effect and must be ``True`` |
| (the default). |
| |
| A custom opener can be used by passing a callable as *opener*. The underlying |
| file descriptor for the file object is then obtained by calling *opener* with |
| (*file*, *flags*). *opener* must return an open file descriptor (passing |
| :mod:`os.open` as *opener* results in functionality similar to passing |
| ``None``). |
| |
| .. versionchanged:: 3.3 |
| The *opener* parameter was added. |
| |
| The type of file object returned by the :func:`open` function depends on the |
| mode. When :func:`open` is used to open a file in a text mode (``'w'``, |
| ``'r'``, ``'wt'``, ``'rt'``, etc.), it returns a subclass of |
| :class:`io.TextIOBase` (specifically :class:`io.TextIOWrapper`). When used |
| to open a file in a binary mode with buffering, the returned class is a |
| subclass of :class:`io.BufferedIOBase`. The exact class varies: in read |
| binary mode, it returns a :class:`io.BufferedReader`; in write binary and |
| append binary modes, it returns a :class:`io.BufferedWriter`, and in |
| read/write mode, it returns a :class:`io.BufferedRandom`. When buffering is |
| disabled, the raw stream, a subclass of :class:`io.RawIOBase`, |
| :class:`io.FileIO`, is returned. |
| |
| .. index:: |
| single: line-buffered I/O |
| single: unbuffered I/O |
| single: buffer size, I/O |
| single: I/O control; buffering |
| single: binary mode |
| single: text mode |
| module: sys |
| |
| See also the file handling modules, such as, :mod:`fileinput`, :mod:`io` |
| (where :func:`open` is declared), :mod:`os`, :mod:`os.path`, :mod:`tempfile`, |
| and :mod:`shutil`. |
| |
| .. versionchanged:: 3.3 |
| :exc:`IOError` used to be raised, it is now an alias of :exc:`OSError`. |
| |
| |
| .. XXX works for bytes too, but should it? |
| .. function:: ord(c) |
| |
| Given a string representing one Unicode character, return an integer |
| representing the Unicode code |
| point of that character. For example, ``ord('a')`` returns the integer ``97`` |
| and ``ord('\u2020')`` returns ``8224``. This is the inverse of :func:`chr`. |
| |
| |
| .. function:: pow(x, y[, z]) |
| |
| Return *x* to the power *y*; if *z* is present, return *x* to the power *y*, |
| modulo *z* (computed more efficiently than ``pow(x, y) % z``). The two-argument |
| form ``pow(x, y)`` is equivalent to using the power operator: ``x**y``. |
| |
| The arguments must have numeric types. With mixed operand types, the |
| coercion rules for binary arithmetic operators apply. For :class:`int` |
| operands, the result has the same type as the operands (after coercion) |
| unless the second argument is negative; in that case, all arguments are |
| converted to float and a float result is delivered. For example, ``10**2`` |
| returns ``100``, but ``10**-2`` returns ``0.01``. If the second argument is |
| negative, the third argument must be omitted. If *z* is present, *x* and *y* |
| must be of integer types, and *y* must be non-negative. |
| |
| |
| .. function:: print([object, ...], *, sep=' ', end='\\n', file=sys.stdout, flush=False) |
| |
| Print *object*\(s) to the stream *file*, separated by *sep* and followed by |
| *end*. *sep*, *end* and *file*, if present, must be given as keyword |
| arguments. |
| |
| All non-keyword arguments are converted to strings like :func:`str` does and |
| written to the stream, separated by *sep* and followed by *end*. Both *sep* |
| and *end* must be strings; they can also be ``None``, which means to use the |
| default values. If no *object* is given, :func:`print` will just write |
| *end*. |
| |
| The *file* argument must be an object with a ``write(string)`` method; if it |
| is not present or ``None``, :data:`sys.stdout` will be used. Whether output |
| is buffered is usually determined by *file*, but if the *flush* keyword |
| argument is true, the stream is forcibly flushed. |
| |
| .. versionchanged:: 3.3 |
| Added the *flush* keyword argument. |
| |
| |
| .. function:: property(fget=None, fset=None, fdel=None, doc=None) |
| |
| 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: |
| def __init__(self): |
| self._x = None |
| |
| def getx(self): |
| return self._x |
| def setx(self, value): |
| self._x = value |
| def delx(self): |
| del self._x |
| x = property(getx, setx, delx, "I'm the 'x' property.") |
| |
| If then *c* is an instance of *C*, ``c.x`` will invoke the getter, |
| ``c.x = value`` will invoke the setter and ``del c.x`` the deleter. |
| |
| If given, *doc* will be the docstring of the property attribute. Otherwise, the |
| property will copy *fget*'s docstring (if it exists). This makes it possible to |
| create read-only properties easily using :func:`property` as a :term:`decorator`:: |
| |
| class Parrot: |
| def __init__(self): |
| self._voltage = 100000 |
| |
| @property |
| def voltage(self): |
| """Get the current voltage.""" |
| return self._voltage |
| |
| turns the :meth:`voltage` method into a "getter" for a read-only attribute |
| with the same name. |
| |
| A property object has :attr:`getter`, :attr:`setter`, and :attr:`deleter` |
| methods usable as decorators that create a copy of the property with the |
| corresponding accessor function set to the decorated function. This is |
| best explained with an example:: |
| |
| class C: |
| def __init__(self): |
| self._x = None |
| |
| @property |
| def x(self): |
| """I'm the 'x' property.""" |
| return self._x |
| |
| @x.setter |
| def x(self, value): |
| self._x = value |
| |
| @x.deleter |
| def x(self): |
| del self._x |
| |
| This code is exactly equivalent to the first example. Be sure to give the |
| additional functions the same name as the original property (``x`` in this |
| case.) |
| |
| The returned property also has the attributes ``fget``, ``fset``, and |
| ``fdel`` corresponding to the constructor arguments. |
| |
| |
| .. XXX does accept objects with __index__ too |
| .. function:: range([start,] stop[, step]) |
| |
| This is a versatile function to create iterables yielding arithmetic |
| progressions. It is most often used in :keyword:`for` loops. The arguments |
| must be integers. If the *step* argument is omitted, it defaults to ``1``. |
| If the *start* argument is omitted, it defaults to ``0``. The full form |
| returns an iterable of integers ``[start, start + step, start + 2 * step, |
| ...]``. If *step* is positive, the last element is the largest ``start + i * |
| step`` less than *stop*; if *step* is negative, the last element is the |
| smallest ``start + i * step`` greater than *stop*. *step* must not be zero |
| (or else :exc:`ValueError` is raised). Range objects have read-only data |
| attributes :attr:`start`, :attr:`stop` and :attr:`step` which return the |
| argument values (or their default). 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)) |
| [] |
| |
| Range objects implement the :class:`collections.Sequence` ABC, and provide |
| features such as containment tests, element index lookup, slicing and |
| support for negative indices (see :ref:`typesseq`): |
| |
| >>> r = range(0, 20, 2) |
| >>> r |
| range(0, 20, 2) |
| >>> 11 in r |
| False |
| >>> 10 in r |
| True |
| >>> r.index(10) |
| 5 |
| >>> r[5] |
| 10 |
| >>> r[:5] |
| range(0, 10, 2) |
| >>> r[-1] |
| 18 |
| |
| Testing range objects for equality with ``==`` and ``!=`` compares |
| them as sequences. That is, two range objects are considered equal if |
| they represent the same sequence of values. (Note that two range |
| objects that compare equal might have different :attr:`start`, |
| :attr:`stop` and :attr:`step` attributes, for example ``range(0) == |
| range(2, 1, 3)`` or ``range(0, 3, 2) == range(0, 4, 2)``.) |
| |
| Ranges containing absolute values larger than :data:`sys.maxsize` are permitted |
| but some features (such as :func:`len`) will raise :exc:`OverflowError`. |
| |
| .. versionchanged:: 3.2 |
| Implement the Sequence ABC. |
| Support slicing and negative indices. |
| Test integers for membership in constant time instead of iterating |
| through all items. |
| |
| .. versionchanged:: 3.3 |
| Define '==' and '!=' to compare range objects based on the |
| sequence of values they define (instead of comparing based on |
| object identity). |
| |
| .. versionadded:: 3.3 |
| The :attr:`start`, :attr:`stop` and :attr:`step` attributes. |
| |
| |
| .. function:: repr(object) |
| |
| Return a string containing a printable representation of an object. For many |
| types, this function makes an attempt to return a string that would yield an |
| object with the same value when passed to :func:`eval`, otherwise the |
| representation is a string enclosed in angle brackets that contains the name |
| of the type of the object together with additional information often |
| including the name and address of the object. A class can control what this |
| function returns for its instances by defining a :meth:`__repr__` method. |
| |
| |
| .. function:: reversed(seq) |
| |
| Return a reverse :term:`iterator`. *seq* must be an object which has |
| a :meth:`__reversed__` method or supports the sequence protocol (the |
| :meth:`__len__` method and the :meth:`__getitem__` method with integer |
| arguments starting at ``0``). |
| |
| |
| .. function:: round(x[, n]) |
| |
| Return the floating point value *x* rounded to *n* digits after the decimal |
| point. If *n* is omitted, it defaults to zero. Delegates to |
| ``x.__round__(n)``. |
| |
| For the built-in types supporting :func:`round`, values are rounded to the |
| closest multiple of 10 to the power minus *n*; if two multiples are equally |
| close, rounding is done toward the even choice (so, for example, both |
| ``round(0.5)`` and ``round(-0.5)`` are ``0``, and ``round(1.5)`` is ``2``). |
| The return value is an integer if called with one argument, otherwise of the |
| same type as *x*. |
| |
| .. note:: |
| |
| The behavior of :func:`round` for floats can be surprising: for example, |
| ``round(2.675, 2)`` gives ``2.67`` instead of the expected ``2.68``. |
| This is not a bug: it's a result of the fact that most decimal fractions |
| can't be represented exactly as a float. See :ref:`tut-fp-issues` for |
| more information. |
| |
| |
| .. _func-set: |
| .. function:: set([iterable]) |
| :noindex: |
| |
| Return a new set, optionally with elements taken from *iterable*. |
| The set type is described in :ref:`types-set`. |
| |
| |
| .. function:: setattr(object, name, value) |
| |
| This is the counterpart of :func:`getattr`. The arguments are an object, a |
| string and an arbitrary value. The string may name an existing attribute or a |
| new attribute. The function assigns the value to the attribute, provided the |
| object allows it. For example, ``setattr(x, 'foobar', 123)`` is equivalent to |
| ``x.foobar = 123``. |
| |
| |
| .. function:: slice([start,] stop[, step]) |
| |
| .. index:: single: Numerical Python |
| |
| Return a :term:`slice` object representing the set of indices specified by |
| ``range(start, stop, step)``. The *start* and *step* arguments default to |
| ``None``. Slice objects have read-only data attributes :attr:`start`, |
| :attr:`stop` and :attr:`step` which merely return the argument values (or their |
| default). They have no other explicit functionality; however they are used by |
| Numerical Python and other third party extensions. Slice objects are also |
| generated when extended indexing syntax is used. For example: |
| ``a[start:stop:step]`` or ``a[start:stop, i]``. See :func:`itertools.islice` |
| for an alternate version that returns an iterator. |
| |
| |
| .. function:: sorted(iterable[, key][, reverse]) |
| |
| Return a new sorted list from the items in *iterable*. |
| |
| Has two optional arguments which must be specified as keyword arguments. |
| |
| *key* specifies a function of one argument that is used to extract a comparison |
| key from each list element: ``key=str.lower``. The default value is ``None`` |
| (compare the elements directly). |
| |
| *reverse* is a boolean value. If set to ``True``, then the list elements are |
| sorted as if each comparison were reversed. |
| |
| Use :func:`functools.cmp_to_key` to convert an old-style *cmp* function to a |
| *key* function. |
| |
| For sorting examples and a brief sorting tutorial, see `Sorting HowTo |
| <http://wiki.python.org/moin/HowTo/Sorting/>`_\. |
| |
| .. function:: staticmethod(function) |
| |
| Return a static method for *function*. |
| |
| A static method does not receive an implicit first argument. To declare a static |
| method, use this idiom:: |
| |
| class C: |
| @staticmethod |
| def f(arg1, arg2, ...): ... |
| |
| The ``@staticmethod`` form is a function :term:`decorator` -- see the |
| description of function definitions in :ref:`function` for details. |
| |
| It can be called either on the class (such as ``C.f()``) or on an instance (such |
| as ``C().f()``). The instance is ignored except for its class. |
| |
| Static methods in Python are similar to those found in Java or C++. Also see |
| :func:`classmethod` for a variant that is useful for creating alternate class |
| constructors. |
| |
| For more information on static methods, consult the documentation on the |
| standard type hierarchy in :ref:`types`. |
| |
| |
| .. 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 the start value is not allowed to be a string. |
| |
| For some use cases, there are good alternatives to :func:`sum`. |
| The preferred, fast way to concatenate a sequence of strings is by calling |
| ``''.join(sequence)``. To add floating point values with extended precision, |
| see :func:`math.fsum`\. To concatenate a series of iterables, consider using |
| :func:`itertools.chain`. |
| |
| .. function:: super([type[, object-or-type]]) |
| |
| Return a proxy object that delegates method calls to a parent or sibling |
| class of *type*. This is useful for accessing inherited methods that have |
| been overridden in a class. The search order is same as that used by |
| :func:`getattr` except that the *type* itself is skipped. |
| |
| The :attr:`__mro__` attribute of the *type* lists the method resolution |
| search order used by both :func:`getattr` and :func:`super`. The attribute |
| is dynamic and can change whenever the inheritance hierarchy is updated. |
| |
| If the second argument is omitted, the super object returned is unbound. If |
| the second argument is an object, ``isinstance(obj, type)`` must be true. If |
| the second argument is a type, ``issubclass(type2, type)`` must be true (this |
| is useful for classmethods). |
| |
| There are two typical use cases for *super*. In a class hierarchy with |
| single inheritance, *super* can be used to refer to parent classes without |
| naming them explicitly, thus making the code more maintainable. This use |
| closely parallels the use of *super* in other programming languages. |
| |
| The second use case is to support cooperative multiple inheritance in a |
| dynamic execution environment. This use case is unique to Python and is |
| not found in statically compiled languages or languages that only support |
| single inheritance. This makes it possible to implement "diamond diagrams" |
| where multiple base classes implement the same method. Good design dictates |
| that this method have the same calling signature in every case (because the |
| order of calls is determined at runtime, because that order adapts |
| to changes in the class hierarchy, and because that order can include |
| sibling classes that are unknown prior to runtime). |
| |
| For both use cases, a typical superclass call looks like this:: |
| |
| class C(B): |
| def method(self, arg): |
| super().method(arg) # This does the same thing as: |
| # super(C, self).method(arg) |
| |
| Note that :func:`super` is implemented as part of the binding process for |
| explicit dotted attribute lookups such as ``super().__getitem__(name)``. |
| It does so by implementing its own :meth:`__getattribute__` method for searching |
| classes in a predictable order that supports cooperative multiple inheritance. |
| Accordingly, :func:`super` is undefined for implicit lookups using statements or |
| operators such as ``super()[name]``. |
| |
| Also note that :func:`super` is not limited to use inside methods. The two |
| argument form specifies the arguments exactly and makes the appropriate |
| references. The zero argument form automatically searches the stack frame |
| for the class (``__class__``) and the first argument. |
| |
| For practical suggestions on how to design cooperative classes using |
| :func:`super`, see `guide to using super() |
| <http://rhettinger.wordpress.com/2011/05/26/super-considered-super/>`_. |
| |
| |
| .. function:: tuple([iterable]) |
| |
| Return a tuple whose items are the same and in the same order as *iterable*'s |
| items. *iterable* may be a sequence, a container that supports iteration, or an |
| iterator object. If *iterable* is already a tuple, it is returned unchanged. |
| For instance, ``tuple('abc')`` returns ``('a', 'b', 'c')`` and ``tuple([1, 2, |
| 3])`` returns ``(1, 2, 3)``. If no argument is given, returns a new empty |
| tuple, ``()``. |
| |
| :class:`tuple` is an immutable sequence type, as documented in :ref:`typesseq`. |
| |
| |
| .. function:: type(object) |
| |
| .. index:: object: type |
| |
| Return the type of an *object*. The return value is a type object and |
| generally the same object as returned by ``object.__class__``. |
| |
| The :func:`isinstance` built-in function is recommended for testing the type |
| of an object, because it takes subclasses into account. |
| |
| With three arguments, :func:`type` functions as a constructor as detailed |
| below. |
| |
| |
| .. function:: type(name, bases, dict) |
| :noindex: |
| |
| Return a new type object. This is essentially a dynamic form of the |
| :keyword:`class` statement. The *name* string is the class name and becomes the |
| :attr:`__name__` attribute; the *bases* tuple itemizes the base classes and |
| becomes the :attr:`__bases__` attribute; and the *dict* dictionary is the |
| namespace containing definitions for class body and becomes the :attr:`__dict__` |
| attribute. For example, the following two statements create identical |
| :class:`type` objects: |
| |
| >>> class X: |
| ... a = 1 |
| ... |
| >>> X = type('X', (object,), dict(a=1)) |
| |
| |
| .. function:: vars([object]) |
| |
| Without an argument, act like :func:`locals`. |
| |
| With a module, class or class instance object as argument (or anything else that |
| has a :attr:`__dict__` attribute), return that attribute. |
| |
| .. note:: |
| The returned dictionary should not be modified: |
| the effects on the corresponding symbol table are undefined. [#]_ |
| |
| .. function:: zip(*iterables) |
| |
| Make an iterator that aggregates elements from each of the iterables. |
| |
| Returns an iterator of tuples, where the *i*-th tuple contains |
| the *i*-th element from each of the argument sequences or iterables. The |
| iterator stops when the shortest input iterable is exhausted. With a single |
| iterable argument, it returns an iterator of 1-tuples. With no arguments, |
| it returns an empty iterator. Equivalent to:: |
| |
| def zip(*iterables): |
| # zip('ABCD', 'xy') --> Ax By |
| sentinel = object() |
| iterators = [iter(it) for it in iterables] |
| while iterators: |
| result = [] |
| for it in iterators: |
| elem = next(it, sentinel) |
| if elem is sentinel: |
| return |
| result.append(elem) |
| yield tuple(result) |
| |
| The left-to-right evaluation order of the iterables is guaranteed. This |
| makes possible an idiom for clustering a data series into n-length groups |
| using ``zip(*[iter(s)]*n)``. |
| |
| :func:`zip` should only be used with unequal length inputs when you don't |
| care about trailing, unmatched values from the longer iterables. If those |
| values are important, use :func:`itertools.zip_longest` instead. |
| |
| :func:`zip` in conjunction with the ``*`` operator can be used to unzip a |
| list:: |
| |
| >>> x = [1, 2, 3] |
| >>> y = [4, 5, 6] |
| >>> zipped = zip(x, y) |
| >>> list(zipped) |
| [(1, 4), (2, 5), (3, 6)] |
| >>> x2, y2 = zip(*zip(x, y)) |
| >>> x == list(x2) and y == list(y2) |
| True |
| |
| |
| .. function:: __import__(name, globals={}, locals={}, fromlist=[], level=0) |
| |
| .. index:: |
| statement: import |
| module: imp |
| |
| .. note:: |
| |
| This is an advanced function that is not needed in everyday Python |
| programming, unlike :func:`importlib.import_module`. |
| |
| This function is invoked by the :keyword:`import` statement. It can be |
| replaced (by importing the :mod:`builtins` module and assigning to |
| ``builtins.__import__``) in order to change semantics of the |
| :keyword:`import` statement, but nowadays it is usually simpler to use import |
| hooks (see :pep:`302`) to attain the same goals. Direct use of |
| :func:`__import__` is entirely discouraged in favor of |
| :func:`importlib.import_module`. |
| |
| The function imports the module *name*, potentially using the given *globals* |
| and *locals* to determine how to interpret the name in a package context. |
| The *fromlist* gives the names of objects or submodules that should be |
| imported from the module given by *name*. The standard implementation does |
| not use its *locals* argument at all, and uses its *globals* only to |
| determine the package context of the :keyword:`import` statement. |
| |
| *level* specifies whether to use absolute or relative imports. ``0`` (the |
| default) 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__` (see :pep:`328` for the |
| details). |
| |
| When the *name* variable is of the form ``package.module``, normally, the |
| top-level package (the name up till the first dot) is returned, *not* the |
| module named by *name*. However, when a non-empty *fromlist* argument is |
| given, the module named by *name* is returned. |
| |
| For example, the statement ``import spam`` results in bytecode resembling the |
| following code:: |
| |
| spam = __import__('spam', globals(), locals(), [], 0) |
| |
| The statement ``import spam.ham`` results in this call:: |
| |
| spam = __import__('spam.ham', globals(), locals(), [], 0) |
| |
| Note how :func:`__import__` returns the toplevel module here because this is |
| the object that is bound to a name by the :keyword:`import` statement. |
| |
| On the other hand, the statement ``from spam.ham import eggs, sausage as |
| saus`` results in :: |
| |
| _temp = __import__('spam.ham', globals(), locals(), ['eggs', 'sausage'], 0) |
| eggs = _temp.eggs |
| saus = _temp.sausage |
| |
| Here, the ``spam.ham`` module is returned from :func:`__import__`. From this |
| object, the names to import are retrieved and assigned to their respective |
| names. |
| |
| If you simply want to import a module (potentially within a package) by name, |
| use :func:`importlib.import_module`. |
| |
| |
| .. rubric:: Footnotes |
| |
| .. [#] Note that the parser only accepts the Unix-style end of line convention. |
| If you are reading the code from a file, make sure to use newline conversion |
| mode to convert Windows or Mac-style newlines. |
| |
| .. [#] 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. |