.. 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.

+---------------------------- | +=========================+== | | A | | :func:abs | | :func:aiter | | :func:all | | :func:anext | | :func:any | | :func:ascii | | | | B | | :func:bin | | :func:bool | | :func:breakpoint | | |func-bytearray|_ | | |func-bytes|_ | | | | | | C | | :func:callable | | :func:chr | | :func:classmethod | | :func:compile | | :func:complex | | | | D | | :func:delattr | | |func-dict|_ | | :func:dir | | :func:divmod | | +-------------------------+-- -----------------------------------------------------------------------+ Built-in Functions | =====================+=======================+=========================+ | | E | | L | | R | | | :func:enumerate | | :func:len | | |func-range|_ | | | :func:eval | | |func-list|_ | | :func:repr | | | :func:exec | | :func:locals | | :func:reversed | | | | | | | :func:round | | | F | | M | | | | | :func:filter | | :func:map | | S | | | :func:float | | :func:max | | |func-set|_ | | | :func:format | | |func-memoryview|_ | | :func:setattr | | | |func-frozenset|_ | | :func:min | | :func:slice | | | | | | | :func:sorted | | | G | | N | | :func:staticmethod | | | :func:getattr | | :func:next | | |func-str|_ | | | :func:globals | | | | :func:sum | | | O | | :func:super | | | H | | :func:object | | | | | :func:hasattr | | :func:oct | | T | | | :func:hash | | :func:open | | |func-tuple|_ | | | :func:help | | :func:ord | | :func:type | | | :func:hex | | | | | | | | | P | | V | | | I | | :func:pow | | :func:vars | | | :func:id | | :func:print | | | | | :func:input | | :func:property | | Z | | | :func:int | | | | :func:zip | | | :func:isinstance | | | | | | | :func:issubclass | | | | _ | | | :func:iter | | | | :func:__import__ | ---------------------+-----------------------+-------------------------+

.. 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

.. function:: abs(number, /)

Return the absolute value of a number. The argument may be an integer, a floating-point number, or an object implementing :meth:~object.__abs__. If the argument is a complex number, its magnitude is returned.

.. function:: aiter(async_iterable, /)

Return an :term:asynchronous iterator for an :term:asynchronous iterable. Equivalent to calling x.__aiter__().

Note: Unlike :func:iter, :func:aiter has no 2-argument variant.

.. versionadded:: 3.10

.. 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

.. awaitablefunction:: anext(async_iterator, /) anext(async_iterator, default, /)

When awaited, return the next item from the given :term:asynchronous iterator, or default if given and the iterator is exhausted.

This is the async variant of the :func:next builtin, and behaves similarly.

This calls the :meth:~object.__anext__ method of async_iterator, returning an :term:awaitable. Awaiting this returns the next value of the iterator. If default is given, it is returned if the iterator is exhausted, otherwise :exc:StopAsyncIteration is raised.

.. versionadded:: 3.10

.. 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(integer, /)

Convert an integer number to a binary string prefixed with "0b". The result is a valid Python expression. If integer is not a Python :class:int object, it has to define an :meth:~object.__index__ method that returns an integer. Some examples:

  >>> bin(3)
  '0b11'
  >>> bin(-10)
  '-0b1010'

If the prefix "0b" is desired or not, you can use either of the following ways.

  >>> format(14, '#b'), format(14, 'b')
  ('0b1110', '1110')
  >>> f'{14:#b}', f'{14:b}'
  ('0b1110', '1110')

See also :func:enum.bin to represent negative values as twos-complement.

See also :func:format for more information.

.. class:: bool(object=False, /)

Return a Boolean value, i.e. one of True or False. The argument is converted using the standard :ref:truth testing procedure <truth>. If the argument is false or omitted, this returns False; otherwise, it returns True. The :class:bool class is a subclass of :class:int (see :ref:typesnumeric). It cannot be subclassed further. Its only instances are False and True (see :ref:typebool).

.. index:: pair: Boolean; type

.. versionchanged:: 3.7 The parameter is now positional-only.

.. function:: breakpoint(*args, **kws)

This function drops you into the debugger at the call site. Specifically, it calls :func:sys.breakpointhook, passing args and kws straight through. By default, sys.breakpointhook() calls :func:pdb.set_trace expecting no arguments. In this case, it is purely a convenience function so you don't have to explicitly import :mod:pdb or type as much code to enter the debugger. However, :func:sys.breakpointhook can be set to some other function and :func:breakpoint will automatically call that, allowing you to drop into the debugger of choice. If :func:sys.breakpointhook is not accessible, this function will raise :exc:RuntimeError.

By default, the behavior of :func:breakpoint can be changed with the :envvar:PYTHONBREAKPOINT environment variable. See :func:sys.breakpointhook for usage details.

Note that this is not guaranteed if :func:sys.breakpointhook has been replaced.

.. audit-event:: builtins.breakpoint breakpointhook breakpoint

.. versionadded:: 3.7

.. _func-bytearray: .. class:: bytearray(source=b'') bytearray(source, encoding, errors='strict') :noindex:

Return a new array of bytes. The :class:bytearray class 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 :ref:buffer interface <bufferobjects>, 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.

See also :ref:binaryseq and :ref:typebytearray.

.. _func-bytes: .. class:: bytes(source=b'') bytes(source, encoding, errors='strict') :noindex:

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.

See also :ref:binaryseq, :ref:typebytes, and :ref:bytes-methods.

.. 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:~object.__call__ method.

.. versionadded:: 3.2 This function was first removed in Python 3.0 and then brought back in Python 3.2.

.. function:: chr(codepoint, /)

Return the string representing a character with the specified Unicode code point. For example, chr(97) returns the string 'a', while chr(8364) returns the string '€'. 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 it is outside that range.

.. decorator:: classmethod

Transform a method into a class method.

A class method receives the class as an 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 :ref:function for details.

A class method 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, see :ref:types.

.. versionchanged:: 3.9 Class methods can now wrap other :term:descriptors <descriptor> such as :func:property.

.. versionchanged:: 3.10 Class methods now inherit the method attributes (:attr:~function.__module__, :attr:~function.__name__, :attr:~function.__qualname__, :attr:~function.__doc__ and :attr:~function.__annotations__) and have a new __wrapped__ attribute.

.. deprecated-removed:: 3.11 3.13 Class methods can no longer wrap other :term:descriptors <descriptor> such as :func:property.

.. function:: compile(source, filename, mode, flags=0,
dont_inherit=False, optimize=-1,
*, module=None)

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 normal string, a byte 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 :ref:compiler options <ast-compiler-flags> should be activated and which :ref:future features <future> should be allowed. If neither is present (or both are zero) the code is compiled with the same flags that affect the code that is calling :func:compile. If the flags argument is given and dont_inherit is not (or is zero) then the compiler options and 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 flags (future features and compiler options) in the surrounding code are ignored.

Compiler options and future statements are specified by bits which can be bitwise ORed together to specify multiple options. The bitfield required to specify a given future feature can be found as the :attr:~__future__._Feature.compiler_flag attribute on the :class:~__future__._Feature instance in the :mod:__future__ module. :ref:Compiler flags <ast-compiler-flags> can be found in :mod:ast module, with PyCF_ prefix.

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).

The optional argument module specifies the module name. It is needed to unambiguous :ref:filter <warning-filter> syntax warnings by module name.

This function raises :exc:SyntaxError or :exc:ValueError if the compiled source is invalid.

If you want to parse Python code into its AST representation, see :func:ast.parse.

.. audit-event:: compile source,filename compile

  Raises an :ref:`auditing event <auditing>` ``compile`` with arguments
  ``source`` and ``filename``. This event may also be raised by implicit
  compilation.

.. 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.

.. warning::

  It is possible to crash the Python interpreter with a
  sufficiently large/complex string when compiling to an AST
  object due to stack depth limitations in Python's AST compiler.

.. 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.

.. versionchanged:: 3.5 Previously, :exc:TypeError was raised when null bytes were encountered in source.

.. versionadded:: 3.8 ast.PyCF_ALLOW_TOP_LEVEL_AWAIT can now be passed in flags to enable support for top-level await, async for, and async with.

.. versionadded:: 3.15 Added the module parameter.

.. class:: complex(number=0, /) complex(string, /) complex(real=0, imag=0)

Convert a single string or number to a complex number, or create a complex number from real and imaginary parts.

Examples:

.. doctest::

  >>> complex('+1.23')
  (1.23+0j)
  >>> complex('-4.5j')
  -4.5j
  >>> complex('-1.23+4.5j')
  (-1.23+4.5j)
  >>> complex('\t( -1.23+4.5J )\n')
  (-1.23+4.5j)
  >>> complex('-Infinity+NaNj')
  (-inf+nanj)
  >>> complex(1.23)
  (1.23+0j)
  >>> complex(imag=-4.5)
  -4.5j
  >>> complex(-1.23, 4.5)
  (-1.23+4.5j)

If the argument is a string, it must contain either a real part (in the same format as for :func:float) or an imaginary part (in the same format but with a 'j' or 'J' suffix), or both real and imaginary parts (the sign of the imaginary part is mandatory in this case). The string can optionally be surrounded by whitespaces and the round parentheses '(' and ')', which are ignored. The string must not contain whitespace between '+', '-', the 'j' or 'J' suffix, and the decimal number. For example, complex('1+2j') is fine, but complex('1 + 2j') raises :exc:ValueError. More precisely, the input must conform to the :token:~float:complexvalue production rule in the following grammar, after parentheses and leading and trailing whitespace characters are removed:

.. productionlist:: float complexvalue: floatvalue | : floatvalue ("j" | "J") | : floatvalue sign absfloatvalue ("j" | "J")

If the argument is a number, the constructor serves as a numeric conversion like :class:int and :class:float. For a general Python object x, complex(x) delegates to x.__complex__(). If :meth:~object.__complex__ is not defined then it falls back to :meth:~object.__float__. If :meth:!__float__ is not defined then it falls back to :meth:~object.__index__.

If two arguments are provided or keyword arguments are used, each argument may be any numeric type (including complex). If both arguments are real numbers, return a complex number with the real component real and the imaginary component imag. If both arguments are complex numbers, return a complex number with the real component real.real-imag.imag and the imaginary component real.imag+imag.real. If one of arguments is a real number, only its real component is used in the above expressions.

See also :meth:complex.from_number which only accepts a single numeric argument.

If all arguments are omitted, returns 0j.

The complex type is described in :ref:typesnumeric.

.. versionchanged:: 3.6 Grouping digits with underscores as in code literals is allowed.

.. versionchanged:: 3.8 Falls back to :meth:~object.__index__ if :meth:~object.__complex__ and :meth:~object.__float__ are not defined.

.. deprecated:: 3.14 Passing a complex number as the real or imag argument is now deprecated; it should only be passed as a single positional argument.

.. 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. name need not be a Python identifier (see :func:setattr).

.. _func-dict: .. class:: dict(**kwargs) dict(mapping, /, **kwargs) dict(iterable, /, **kwargs) :noindex:

Create a new dictionary. The :class:dict object is the dictionary class. See :class:dict and :ref:typesmapping for documentation about this class.

For other containers see the built-in :class:list, :class:set, and :class:tuple classes, as well as the :mod:collections module.

.. function:: dir() 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:~object.__dir__, this method will be called and must return the list of attributes. This allows objects that implement a custom :func:~object.__getattr__ or :func:~object.__getattribute__ function to customize the way :func:dir reports their attributes.

If the object does not provide :meth:~object.__dir__, the function tries its best to gather information from the object's :attr:~object.__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:~object.__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  # doctest: +SKIP
  ['__builtins__', '__name__', 'struct']
  >>> dir(struct)   # show the names in the struct module # doctest: +SKIP
  ['Struct', '__all__', '__builtins__', '__doc__', '__file__',
   '__initializing__', '__loader__', '__name__', '__package__',
   '_clearcache', 'calcsize', 'error', 'pack', 'pack_into',
   'unpack', 'unpack_from']
  >>> class Shape:
  ...     def __dir__(self):
  ...         return ['area', 'perimeter', 'location']
  ...
  >>> s = Shape()
  >>> dir(s)
  ['area', 'location', 'perimeter']

.. 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:~iterator.__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(iterable, start=0):
      n = start
      for elem in iterable:
          yield n, elem
          n += 1

.. _func-eval:

.. function:: eval(source, /, globals=None, locals=None)

:param source: A Python expression. :type source: :class:str | :ref:code object <code-objects>

:param globals: The global namespace (default: None). :type globals: :class:dict | :class:frozendict | None

:param locals: The local namespace (default: None). :type locals: :term:mapping | None

:returns: The result of the evaluated expression. :raises: Syntax errors are reported as exceptions.

.. warning::

  This function executes arbitrary code. Calling it with
  untrusted user-supplied input will lead to security vulnerabilities.

The source argument is parsed and evaluated as a Python expression (technically speaking, a condition list) using the globals and locals mappings as global and local namespace. If the globals dictionary is present and 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 before source is parsed. Overriding __builtins__ can be used to restrict or change the available names, but this is not a security mechanism: the executed code can still access all builtins. If the locals mapping is omitted it defaults to the globals dictionary. If both mappings are omitted, the source is executed with the globals and locals in the environment where :func:eval is called. Note, eval() will only have access to the :term:nested scopes <nested scope> (non-locals) in the enclosing environment if they are already referenced in the scope that is calling :func:eval (e.g. via a :keyword:nonlocal statement).

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 return the current global and local dictionary, respectively, which may be useful to pass around for use by :func:eval or :func:exec.

If the given source is a string, then leading and trailing spaces and tabs are stripped.

See :func:ast.literal_eval for a function that can safely evaluate strings with expressions containing only literals.

.. audit-event:: exec code_object eval

  Raises an :ref:`auditing event <auditing>` ``exec`` with the code object
  as the argument. Code compilation events may also be raised.

.. versionchanged:: 3.13

  The *globals* and *locals* arguments can now be passed as keywords.

.. versionchanged:: 3.13

  The semantics of the default *locals* namespace have been adjusted as
  described for the :func:`locals` builtin.

.. versionchanged:: 3.15

  *globals* can now be a :class:`frozendict`.

.. index:: pair: built-in function; exec

.. function:: exec(source, /, globals=None, locals=None, *, closure=None)

.. warning::

  This function executes arbitrary code. Calling it with
  untrusted user-supplied input will lead to security vulnerabilities.

This function supports dynamic execution of Python code. source 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 :ref:file-input in the Reference Manual). Be aware that the :keyword:nonlocal, :keyword:yield, and :keyword:return 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 (and not a subclass of 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. Remember that at the module level, globals and locals are the same dictionary.

.. note::

  When ``exec`` gets two separate objects as *globals* and *locals*, the
  code will be executed as if it were embedded in a class definition. This
  means functions and classes defined in the executed code will not be able
  to access variables assigned at the top level (as the "top level"
  variables are treated as class variables in a class definition).

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. Overriding __builtins__ can be used to restrict or change the available names, but this is not a security mechanism: the executed code can still access all builtins.

The closure argument specifies a closure--a tuple of cellvars. It's only valid when the object is a code object containing :term:free (closure) variables <closure variable>. The length of the tuple must exactly match the length of the code object's :attr:~codeobject.co_freevars attribute.

.. audit-event:: exec code_object exec

  Raises an :ref:`auditing event <auditing>` ``exec`` with the code object
  as the argument. Code compilation events may also be raised.

.. note::

  The built-in functions :func:`globals` and :func:`locals` return the current
  global and local namespace, 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.
  Pass an explicit *locals* dictionary if you need to see effects of the
  code on *locals* after function :func:`exec` returns.

.. versionchanged:: 3.11 Added the closure parameter.

.. versionchanged:: 3.13

  The *globals* and *locals* arguments can now be passed as keywords.

.. versionchanged:: 3.13

  The semantics of the default *locals* namespace have been adjusted as
  described for the :func:`locals` builtin.

.. versionchanged:: 3.15

  *globals* can now be a :class:`frozendict`.

.. function:: filter(function, iterable, /)

Construct an iterator from those elements of iterable for which function is 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 is false.

.. class:: float(number=0.0, /) float(string, /)

.. index:: single: NaN single: Infinity

Return a floating-point number constructed from a number or a string.

Examples:

.. doctest::

  >>> float('+1.23')
  1.23
  >>> float('   -12345\n')
  -12345.0
  >>> float('1e-003')
  0.001
  >>> float('+1E6')
  1000000.0
  >>> float('-Infinity')
  -inf

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 positive or negative infinity. More precisely, the input must conform to the :token:~float:floatvalue production rule in the following grammar, after leading and trailing whitespace characters are removed:

.. productionlist:: float sign: "+" | "-" infinity: "Infinity" | "inf" nan: "nan" digit: <a Unicode decimal digit, i.e. characters in Unicode general category Nd> digitpart: digit (["_"] digit)* number: [digitpart] "." digitpart | digitpart ["."] exponent: ("e" | "E") [sign] digitpart floatnumber: number [exponent] absfloatvalue: floatnumber | infinity | nan floatvalue: [sign] absfloatvalue

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 :meth:~object.__float__ is not defined then it falls back to :meth:~object.__index__.

See also :meth:float.from_number which only accepts a numeric argument.

If no argument is given, 0.0 is returned.

The float type is described in :ref:typesnumeric.

.. versionchanged:: 3.6 Grouping digits with underscores as in code literals is allowed.

.. versionchanged:: 3.7 The parameter is now positional-only.

.. versionchanged:: 3.8 Falls back to :meth:~object.__index__ if :meth:~object.__float__ is not defined.

.. index:: single: format single: string; format() (built-in function)

.. function:: format(value, format_spec="", /)

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 :func:str(value) <str>.

A call to format(value, format_spec) is translated to type(value).__format__(value, format_spec) which bypasses the instance dictionary when searching for the value's :meth:~object.__format__ method. A :exc:TypeError exception is raised if the method search reaches :mod:object and the format_spec is non-empty, or if either the format_spec or the return value are not strings.

.. versionchanged:: 3.4 object().__format__(format_spec) raises :exc:TypeError if format_spec is not an empty string.

.. _func-frozenset: .. class:: frozenset(iterable=(), /) :noindex:

Return a new :class:frozenset object, optionally with elements taken from iterable. frozenset is a built-in class. See :class:frozenset and :ref:types-set for documentation about this class.

For other containers see the built-in :class:set, :class:list, :class:tuple, and :class:dict classes, as well as the :mod:collections module.

.. function:: getattr(object, name, /) 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. name need not be a Python identifier (see :func:setattr).

.. note::

  Since :ref:`private name mangling <private-name-mangling>` happens at
  compilation time, one must manually mangle a private attribute's
  (attributes with two leading underscores) name in order to retrieve it with
  :func:`getattr`.

.. function:: globals()

Return the dictionary implementing the current module namespace. For code within functions, this is set when the function is defined and remains the same regardless of where the function 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).

.. note::

  For objects with custom :meth:`~object.__hash__` methods,
  note that :func:`hash`
  truncates the return value based on the bit width of the host machine.

.. function:: help() help(request)

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.

Note that if a slash(/) appears in the parameter list of a function when invoking :func:help, it means that the parameters prior to the slash are positional-only. For more info, see :ref:the FAQ entry on positional-only parameters <faq-positional-only-arguments>.

This function is added to the built-in namespace by the :mod:site module.

.. versionchanged:: 3.4 Changes to :mod:pydoc and :mod:inspect mean that the reported signatures for callables are now more comprehensive and consistent.

.. function:: hex(integer, /)

Convert an integer number to a lowercase hexadecimal string prefixed with "0x". If integer is not a Python :class:int object, it has to define an :meth:~object.__index__ method that returns an integer. Some examples:

  >>> hex(255)
  '0xff'
  >>> hex(-42)
  '-0x2a'

If you want to convert an integer number to an uppercase or lower hexadecimal string with prefix or not, you can use either of the following ways:

 >>> '%#x' % 255, '%x' % 255, '%X' % 255
 ('0xff', 'ff', 'FF')
 >>> format(255, '#x'), format(255, 'x'), format(255, 'X')
 ('0xff', 'ff', 'FF')
 >>> f'{255:#x}', f'{255:x}', f'{255:X}'
 ('0xff', 'ff', 'FF')

See also :func:format for more information.

See also :func:int for converting a hexadecimal string to an integer using a base of 16.

.. 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.

.. audit-event:: builtins.id id id

.. function:: input() 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('--> ')  # doctest: +SKIP
  --> Monty Python's Flying Circus
  >>> s  # doctest: +SKIP
  "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.

.. audit-event:: builtins.input prompt input

  Raises an :ref:`auditing event <auditing>` ``builtins.input`` with
  argument ``prompt`` before reading input

.. audit-event:: builtins.input/result result input

  Raises an :ref:`auditing event <auditing>` ``builtins.input/result``
  with the result after successfully reading input.

.. class:: int(number=0, /) int(string, /, base=10)

Return an integer object constructed from a number or a string, or return 0 if no arguments are given.

Examples:

.. doctest::

  >>> int(123.45)
  123
  >>> int('123')
  123
  >>> int('   -12_345\n')
  -12345
  >>> int('FACE', 16)
  64206
  >>> int('0xface', 0)
  64206
  >>> int('01110011', base=2)
  115

If the argument defines :meth:~object.__int__, int(x) returns x.__int__(). If the argument defines :meth:~object.__index__, it returns x.__index__(). For floating-point numbers, this truncates towards zero.

If the argument is not a number or if base is given, then it must be a string, :class:bytes, or :class:bytearray instance representing an integer in radix base. Optionally, the string can be preceded by + or - (with no space in between), have leading zeros, be surrounded by whitespace, and have single underscores interspersed between digits.

A base-n integer string contains digits, each representing a value from 0 to n-1. The values 0--9 can be represented by any Unicode decimal digit. The values 10--35 can be represented by a to z (or A to Z). The default base is 10. The allowed bases are 0 and 2--36. Base-2, -8, and -16 strings can be optionally prefixed with 0b/0B, 0o/0O, or 0x/0X, as with integer literals in code. For base 0, the string is interpreted in a similar way to an :ref:integer literal in code <integers>, in that the actual base is 2, 8, 10, or 16 as determined by the prefix. Base 0 also disallows leading zeros: int('010', 0) is not legal, while int('010') and int('010', 8) are.

The integer type is described in :ref:typesnumeric.

.. versionchanged:: 3.4 If base is not an instance of :class:int and the base object has a :meth:base.__index__ <object.__index__> method, that method is called to obtain an integer for the base. Previous versions used :meth:base.__int__ <object.__int__> instead of :meth:base.__index__ <object.__index__>.

.. versionchanged:: 3.6 Grouping digits with underscores as in code literals is allowed.

.. versionchanged:: 3.7 The first parameter is now positional-only.

.. versionchanged:: 3.8 Falls back to :meth:~object.__index__ if :meth:~object.__int__ is not defined.

.. versionchanged:: 3.11 :class:int string inputs and string representations can be limited to help avoid denial of service attacks. A :exc:ValueError is raised when the limit is exceeded while converting a string to an :class:int or when converting an :class:int into a string would exceed the limit. See the :ref:integer string conversion length limitation <int_max_str_digits> documentation.

.. versionchanged:: 3.14 :func:int no longer delegates to the :meth:~object.__trunc__ method.

.. 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 a tuple of type objects (or recursively, other such tuples) or a :ref:types-union of multiple types, return True if object is an instance of any of the types. If classinfo is not a type or tuple of types and such tuples, a :exc:TypeError exception is raised. :exc:TypeError may not be raised for an invalid type if an earlier check succeeds.

.. versionchanged:: 3.10 classinfo can be a :ref:types-union.

.. 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 (or recursively, other such tuples) or a :ref:types-union, in which case return True if class is a subclass of any entry in classinfo. In any other case, a :exc:TypeError exception is raised.

.. versionchanged:: 3.10 classinfo can be a :ref:types-union.

.. function:: iter(iterable, /) iter(callable, 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, the single argument must be a collection object which supports the :term:iterable protocol (the :meth:~object.__iter__ method), or it must support the sequence protocol (the :meth:~object.__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 the first argument must be a callable object. The iterator created in this case will call callable with no arguments for each call to its :meth:~iterator.__next__ method; if the value returned is equal to sentinel, :exc:StopIteration will be raised, otherwise the value will be returned.

See also :ref:typeiter.

One useful application of the second form of :func:iter is to build a block-reader. For example, reading fixed-width blocks from a binary database file until the end of file is reached::

  from functools import partial
  with open('mydata.db', 'rb') as f:
      for block in iter(partial(f.read, 64), b''):
          process_block(block)

.. function:: len(object, /)

Return the length (the number of items) of an object. The argument may be a sequence (such as a string, bytes, tuple, list, or range) or a collection (such as a dictionary, set, or frozen set).

.. impl-detail::

  ``len`` raises :exc:`OverflowError` on lengths larger than
  :data:`sys.maxsize`, such as :class:`range(2 ** 100) <range>`.

.. _func-list: .. class:: list(iterable=(), /) :noindex:

Rather than being a function, :class:list is actually a mutable sequence type, as documented in :ref:typesseq-list and :ref:typesseq.

.. function:: locals()

Return a mapping object representing the current local symbol table, with variable names as the keys, and their currently bound references as the values.

At module scope, as well as when using :func:exec or :func:eval with a single namespace, this function returns the same namespace as :func:globals.

At class scope, it returns the namespace that will be passed to the metaclass constructor.

When using exec() or eval() with separate local and global arguments, it returns the local namespace passed in to the function call.

In all of the above cases, each call to locals() in a given frame of execution will return the same mapping object. Changes made through the mapping object returned from locals() will be visible as assigned, reassigned, or deleted local variables, and assigning, reassigning, or deleting local variables will immediately affect the contents of the returned mapping object.

In an :term:optimized scope (including functions, generators, and coroutines), each call to locals() instead returns a fresh dictionary containing the current bindings of the function's local variables and any nonlocal cell references. In this case, name binding changes made via the returned dict are not written back to the corresponding local variables or nonlocal cell references, and assigning, reassigning, or deleting local variables and nonlocal cell references does not affect the contents of previously returned dictionaries.

Calling locals() as part of a comprehension in a function, generator, or coroutine is equivalent to calling it in the containing scope, except that the comprehension's initialised iteration variables will be included. In other scopes, it behaves as if the comprehension were running as a nested function.

Calling locals() as part of a generator expression is equivalent to calling it in a nested generator function.

.. versionchanged:: 3.12 The behaviour of locals() in a comprehension has been updated as described in :pep:709.

.. versionchanged:: 3.13 As part of :pep:667, the semantics of mutating the mapping objects returned from this function are now defined. The behavior in :term:optimized scopes <optimized scope> is now as described above. Aside from being defined, the behaviour in other scopes remains unchanged from previous versions.

.. function:: map(function, iterable, /, *iterables, strict=False)

Return an iterator that applies function to every item of iterable, yielding the results. If additional iterables 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. If strict is True and one of the iterables is exhausted before the others, a :exc:ValueError is raised. For cases where the function inputs are already arranged into argument tuples, see :func:itertools.starmap.

.. versionchanged:: 3.14 Added the strict parameter.

.. function:: max(iterable, /, *, key=None) max(iterable, /, *, default, key=None) max(arg1, arg2, /, *args, key=None)

Return the largest item in an iterable or the largest of two or more arguments.

If one positional argument is provided, it should be an :term:iterable. The largest item in the iterable is returned. If two or more positional arguments are provided, the largest of the positional arguments is returned.

There are two optional keyword-only arguments. The key argument specifies a one-argument ordering function like that used for :meth:list.sort. The default argument specifies an object to return if the provided iterable is empty. If the iterable is empty and default is not provided, a :exc:ValueError is raised.

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).

.. versionchanged:: 3.4 Added the default keyword-only parameter.

.. versionchanged:: 3.8 The key can be None.

.. _func-memoryview: .. class:: memoryview(object) :noindex:

Return a "memory view" object created from the given argument. See :ref:typememoryview for more information.

.. function:: min(iterable, /, *, key=None) min(iterable, /, *, default, key=None) min(arg1, arg2, /, *args, key=None)

Return the smallest item in an iterable or the smallest of two or more arguments.

If one positional argument is provided, it should be an :term:iterable. The smallest item in the iterable is returned. If two or more positional arguments are provided, the smallest of the positional arguments is returned.

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).

.. versionchanged:: 3.4 Added the default keyword-only parameter.

.. versionchanged:: 3.8 The key can be None.

.. function:: next(iterator, /) next(iterator, default, /)

Retrieve the next item from the :term:iterator by calling its :meth:~iterator.__next__ method. If default is given, it is returned if the iterator is exhausted, otherwise :exc:StopIteration is raised.

.. class:: object()

This is the ultimate base class of all other classes. It has methods that are common to all instances of Python classes. When the constructor is called, it returns a new featureless object. The constructor does not accept any arguments.

.. note::

  :class:`object` instances do *not* have :attr:`~object.__dict__`
  attributes, so you can't assign arbitrary attributes to an instance of
  :class:`object`.

.. function:: oct(integer, /)

Convert an integer number to an octal string prefixed with "0o". The result is a valid Python expression. If integer is not a Python :class:int object, it has to define an :meth:~object.__index__ method that returns an integer. For example:

  >>> oct(8)
  '0o10'
  >>> oct(-56)
  '-0o70'

If you want to convert an integer number to an octal string either with the prefix "0o" or not, you can use either of the following ways.

  >>> '%#o' % 10, '%o' % 10
  ('0o12', '12')
  >>> format(10, '#o'), format(10, 'o')
  ('0o12', '12')
  >>> f'{10:#o}', f'{10:o}'
  ('0o12', '12')

See also :func:format for more information.

.. index:: single: file object; open() built-in function

.. function:: open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)

Open file and return a corresponding :term:file object. If the file cannot be opened, an :exc:OSError is raised. See :ref:tut-files for more examples of how to use this function.

file is a :term:path-like 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), 'x' for exclusive creation, 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: :func:locale.getencoding is called to get the current locale encoding. (For reading and writing raw bytes use binary mode and leave encoding unspecified.) The available modes are:

.. _filemodes:

.. index:: pair: file; modes

========= =============================================================== Character Meaning ========= =============================================================== 'r' open for reading (default) 'w' open for writing, truncating the file first 'x' open for exclusive creation, failing if the file already exists 'a' open for writing, appending to the end of file if it exists 'b' binary mode 't' text mode (default) '+' open for updating (reading and writing) ========= ===============================================================

The default mode is 'r' (open for reading text, a synonym of 'rt'). Modes 'w+' and 'w+b' open and truncate the file. Modes 'r+' and 'r+b' open the file with no 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 when writing in text mode), and an integer > 1 to indicate the size in bytes of a fixed-size chunk buffer. Note that specifying a buffer size this way applies for binary buffered I/O, but TextIOWrapper (i.e., files opened with mode='r+') would have another buffering. To disable buffering in TextIOWrapper, consider using the write_through flag for :func:io.TextIOWrapper.reconfigure. 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 max(min(blocksize, 8 MiB), DEFAULT_BUFFER_SIZE) when the device block size is available. On most systems, the buffer will typically be 128 kilobytes long.
"Interactive" text files (files for which :meth:~io.IOBase.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.getencoding returns), but any :term:text 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. A variety of standard error handlers are available, though any error handling name that has been registered with :func:codecs.register_error is also valid. The standard names can be found in :ref:error-handlers.

.. index:: single: universal newlines; open() built-in function

.. _open-newline-parameter:

newline determines how to parse newline characters from the stream. It can be None, '', '\n', '\r', and '\r\n'. It works as follows:

When reading input from the stream, 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 newlines 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.
When writing output to the stream, if newline is None, any '\n' characters written are translated to the system default line separator, :data:os.linesep. If newline is '' or '\n', 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 must be True (the default); otherwise, an error will be raised.

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).

The newly created file is :ref:non-inheritable <fd_inheritance>.

The following example uses the :ref:dir_fd <dir_fd> parameter of the :func:os.open function to open a file relative to a given directory::

  >>> import os
  >>> dir_fd = os.open('somedir', os.O_RDONLY)
  >>> def opener(path, flags):
  ...     return os.open(path, flags, dir_fd=dir_fd)
  ...
  >>> with open('spamspam.txt', 'w', opener=opener) as f:
  ...     print('This will be written to somedir/spamspam.txt', file=f)
  ...
  >>> os.close(dir_fd)  # don't leak a file descriptor

The type of :term: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 an :class:io.BufferedReader; in write binary and append binary modes, it returns an :class:io.BufferedWriter, and in read/write mode, it returns an :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 pair: 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.

.. audit-event:: open path,mode,flags open

The mode and flags arguments may have been modified or inferred from the original call.

.. versionchanged:: 3.3

  * The *opener* parameter was added.
  * The ``'x'`` mode was added.
  * :exc:`IOError` used to be raised, it is now an alias of :exc:`OSError`.
  * :exc:`FileExistsError` is now raised if the file opened in exclusive
    creation mode (``'x'``) already exists.

.. versionchanged:: 3.4

  * The file is now non-inheritable.

.. versionchanged:: 3.5

  * If the system call is interrupted and the signal handler does not raise an
    exception, the function now retries the system call instead of raising an
    :exc:`InterruptedError` exception (see :pep:`475` for the rationale).
  * The ``'namereplace'`` error handler was added.

.. versionchanged:: 3.6

  * Support added to accept objects implementing :class:`os.PathLike`.
  * On Windows, opening a console buffer may return a subclass of
    :class:`io.RawIOBase` other than :class:`io.FileIO`.

.. versionchanged:: 3.11 The 'U' mode has been removed.

.. function:: ord(character, /)

Return the ordinal value of a character.

If the argument is a one-character string, return the Unicode code point of that character. For example, ord('a') returns the integer 97 and ord('€') (Euro sign) returns 8364. This is the inverse of :func:chr.

If the argument is a :class:bytes or :class:bytearray object of length 1, return its single byte value. For example, ord(b'a') returns the integer 97.

.. function:: pow(base, exp, mod=None)

Return base to the power exp; if mod is present, return base to the power exp, modulo mod (computed more efficiently than pow(base, exp) % mod). The two-argument form pow(base, exp) is equivalent to using the power operator: base**exp.

When arguments are builtin 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, pow(10, 2) returns 100, but pow(10, -2) returns 0.01. For a negative base of type :class:int or :class:float and a non-integral exponent, a complex result is delivered. For example, pow(-9, 0.5) returns a value close to 3j. Whereas, for a negative base of type :class:int or :class:float with an integral exponent, a float result is delivered. For example, pow(-9, 2.0) returns 81.0.

For :class:int operands base and exp, if mod is present, mod must also be of integer type and mod must be nonzero. If mod is present and exp is negative, base must be relatively prime to mod. In that case, pow(inv_base, -exp, mod) is returned, where inv_base is an inverse to base modulo mod.

Here's an example of computing an inverse for 38 modulo 97::

  >>> pow(38, -1, mod=97)
  23
  >>> 23 * 38 % 97 == 1
  True

.. versionchanged:: 3.8 For :class:int operands, the three-argument form of pow now allows the second argument to be negative, permitting computation of modular inverses.

.. versionchanged:: 3.8 Allow keyword arguments. Formerly, only positional arguments were supported.

.. function:: print(*objects, sep=' ', end='\n', file=None, flush=False)

Print objects to the text stream file, separated by sep and followed by end. sep, end, file, and flush, if present, must be given as keyword arguments.

All non-keyword arguments are converted to strings like :func:str does and written to the stream, separated by sep and followed by end. Both sep and end must be strings; they can also be None, which means to use the default values. If no objects are given, :func:print will just write end.

The file argument must be an object with a write(string) method; if it is not present or None, :data:sys.stdout will be used. Since printed arguments are converted to text strings, :func:print cannot be used with binary mode file objects. For these, use file.write(...) instead.

Output buffering is usually determined by file. However, if flush is true, the stream is forcibly flushed.

.. versionchanged:: 3.3 Added the flush keyword argument.

.. class:: property(fget=None, fset=None, fdel=None, doc=None)

Return a property attribute.

fget is a function for getting an attribute value. fset is a function for setting an attribute value. fdel is a function for deleting an attribute value. And doc creates a docstring for the attribute.

A 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 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

The @property decorator turns the :meth:!voltage method into a "getter" for a read-only attribute with the same name, and it sets the docstring for voltage to "Get the current voltage."

.. decorator:: property.getter .. decorator:: property.setter .. decorator:: property.deleter

  A property object has ``getter``, ``setter``,
  and ``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:

  .. testcode::

     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 object also has the attributes ``fget``, ``fset``, and
  ``fdel`` corresponding to the constructor arguments.

.. versionchanged:: 3.5 The docstrings of property objects are now writeable.

.. attribute:: name

  Attribute holding the name of the property. The name of the property
  can be changed at runtime.

  .. versionadded:: 3.13

.. _func-range: .. class:: range(stop, /) range(start, stop, step=1, /) :noindex:

Rather than being a function, :class:range is actually an immutable sequence type, as documented in :ref:typesseq-range and :ref:typesseq.

.. 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:~object.__repr__ method. If :func:sys.displayhook is not accessible, this function will raise :exc:RuntimeError.

This class has a custom representation that can be evaluated::

  class Person:
     def __init__(self, name, age):
        self.name = name
        self.age = age

     def __repr__(self):
        return f"Person({self.name!r}, {self.age!r})"

.. function:: reversed(object, /)

Return a reverse :term:iterator. The argument must be an object which has a :meth:~object.__reversed__ method or supports the sequence protocol (the :meth:~object.__len__ method and the :meth:~object.__getitem__ method with integer arguments starting at 0).

.. function:: round(number, ndigits=None)

Return number rounded to ndigits precision after the decimal point. If ndigits is omitted or is None, it returns the nearest integer to its input.

For the built-in types supporting :func:round, values are rounded to the closest multiple of 10 to the power minus ndigits; 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). Any integer value is valid for ndigits (positive, zero, or negative). The return value is an integer if ndigits is omitted or None. Otherwise, the return value has the same type as number.

For a general Python object number, round delegates to number.__round__.

.. 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: .. class:: set(iterable=(), /) :noindex:

Return a new :class:set object, optionally with elements taken from iterable. set is a built-in class. See :class:set and :ref:types-set for documentation about this class.

For other containers see the built-in :class:frozenset, :class:list, :class:tuple, and :class:dict classes, as well as the :mod:collections module.

.. 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.

name need not be a Python identifier as defined in :ref:identifiers unless the object chooses to enforce that, for example in a custom :meth:~object.__getattribute__ or via :attr:~object.__slots__. An attribute whose name is not an identifier will not be accessible using the dot notation, but is accessible through :func:getattr etc..

.. note::

  Since :ref:`private name mangling <private-name-mangling>` happens at
  compilation time, one must manually mangle a private attribute's
  (attributes with two leading underscores) name in order to set it with
  :func:`setattr`.

.. class:: slice(stop, /) slice(start, stop, step=None, /)

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 are also generated when :ref:slicing syntax <slicings> is used. For example: a[start:stop:step] or a[start:stop, i].

See :func:itertools.islice for an alternate version that returns an :term:iterator.

.. attribute:: slice.start slice.stop slice.step

  These read-only attributes are set to the argument values
  (or their default).  They have no other explicit functionality;
  however, they are used by NumPy and other third-party packages.

.. versionchanged:: 3.12 Slice objects are now :term:hashable (provided :attr:~slice.start, :attr:~slice.stop, and :attr:~slice.step are hashable).

.. function:: sorted(iterable, /, *, key=None, reverse=False)

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 element in iterable (for example, 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.

The built-in :func:sorted function is guaranteed to be stable. A sort is stable if it guarantees not to change the relative order of elements that compare equal --- this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade).

The sort algorithm uses only < comparisons between items. While defining an :meth:~object.__lt__ method will suffice for sorting, :PEP:8 recommends that all six :ref:rich comparisons <comparisons> be implemented. This will help avoid bugs when using the same data with other ordering tools such as :func:max that rely on a different underlying method. Implementing all six comparisons also helps avoid confusion for mixed type comparisons which can call the reflected :meth:~object.__gt__ method.

For sorting examples and a brief sorting tutorial, see :ref:sortinghowto.

.. decorator:: staticmethod

Transform a method into a static method.

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, argN): ...

The @staticmethod form is a function :term:decorator -- see :ref:function for details.

A static method can be called either on the class (such as C.f()) or on an instance (such as C().f()). Moreover, the static method :term:descriptor is also callable, so it can be used in the class definition (such as f()).

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.

Like all decorators, it is also possible to call staticmethod as a regular function and do something with its result. This is needed in some cases where you need a reference to a function from a class body and you want to avoid the automatic transformation to instance method. For these cases, use this idiom::

  def regular_function():
      ...

  class C:
      method = staticmethod(regular_function)

For more information on static methods, see :ref:types.

.. versionchanged:: 3.10 Static methods now inherit the method attributes (:attr:~function.__module__, :attr:~function.__name__, :attr:~function.__qualname__, :attr:~function.__doc__ and :attr:~function.__annotations__), have a new __wrapped__ attribute, and are now callable as regular functions.

.. index:: single: string; str() (built-in function)

.. _func-str: .. class:: str(*, encoding='utf-8', errors='strict') str(object) str(object, encoding, errors='strict') str(object, *, errors) :noindex:

Return a :class:str version of object. See :func:str for details.

str is the built-in string :term:class. For general information about strings, see :ref:textseq.

.. function:: sum(iterable, /, start=0)

Sums start and the items of an iterable from left to right and returns the total. 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.

.. versionchanged:: 3.8 The start parameter can be specified as a keyword argument.

.. versionchanged:: 3.12 Summation of floats switched to an algorithm that gives higher accuracy and better commutativity on most builds.

.. versionchanged:: 3.14 Added specialization for summation of complexes, using same algorithm as for summation of floats.

.. class:: super() super(type, object_or_type=None, /)

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 object_or_type determines the :term:method resolution order to be searched. The search starts from the class right after the type.

For example, if :attr:~type.__mro__ of object_or_type is D -> B -> C -> A -> object and the value of type is B, then :func:super searches C -> A -> object.

The :attr:~type.__mro__ attribute of the class corresponding to object_or_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).

When called directly within an ordinary method of a class, both arguments may be omitted ("zero-argument :func:!super"). In this case, type will be the enclosing class, and obj will be the first argument of the immediately enclosing function (typically self). (This means that zero-argument :func:!super will not work as expected within nested functions, including generator expressions, which implicitly create nested functions.)

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 such implementations 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)

In addition to method lookups, :func:super also works for attribute lookups. One possible use case for this is calling :term:descriptors <descriptor> in a parent or sibling class.

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:~object.__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, aside from the zero argument form, :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 only works inside a class definition, as the compiler fills in the necessary details to correctly retrieve the class being defined, as well as accessing the current instance for ordinary methods.

For practical suggestions on how to design cooperative classes using :func:super, see guide to using super() <https://rhettinger.wordpress.com/2011/05/26/super-considered-super/>_.

.. versionchanged:: 3.14 :class:super objects are now :mod:pickleable <pickle> and :mod:copyable <copy>.

.. _func-tuple: .. class:: tuple(iterable=(), /) :noindex:

Rather than being a function, :class:tuple is actually an immutable sequence type, as documented in :ref:typesseq-tuple and :ref:typesseq.

.. class:: type(object, /) type(name, bases, dict, /, **kwargs)

.. index:: pair: object; type

With one argument, return the type of an object. The return value is a type object and generally the same object as returned by :attr: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, 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:~type.__name__ attribute. The bases tuple contains the base classes and becomes the :attr:~type.__bases__ attribute; if empty, :class:object, the ultimate base of all classes, is added. The dict dictionary contains attribute and method definitions for the class body; it may be copied or wrapped before becoming the :attr:~type.__dict__ attribute. The following two statements create identical :class:!type objects:

  >>> class X:
  ...     a = 1
  ...
  >>> X = type('X', (), dict(a=1))