:mod:`operator` --- Standard operators as functions

===================================================

.. module:: operator

   :synopsis: Functions corresponding to the standard operators.

.. sectionauthor:: Skip Montanaro <skip@automatrix.com>

.. testsetup::

   import operator

   from operator import itemgetter

The :mod:`operator` module exports a set of functions implemented in C

corresponding to the intrinsic operators of Python.  For example,

``operator.add(x, y)`` is equivalent to the expression ``x+y``.  The function

names are those used for special class methods; variants without leading and

trailing ``__`` are also provided for convenience.

The functions fall into categories that perform object comparisons, logical

operations, mathematical operations, sequence operations, and abstract type

tests.

The object comparison functions are useful for all objects, and are named after

the rich comparison operators they support:

.. function:: lt(a, b)

              le(a, b)

              eq(a, b)

              ne(a, b)

              ge(a, b)

              gt(a, b)

              __lt__(a, b)

              __le__(a, b)

              __eq__(a, b)

              __ne__(a, b)

              __ge__(a, b)

              __gt__(a, b)

   Perform "rich comparisons" between *a* and *b*. Specifically, ``lt(a, b)`` is

   equivalent to ``a < b``, ``le(a, b)`` is equivalent to ``a <= b``, ``eq(a,

   b)`` is equivalent to ``a == b``, ``ne(a, b)`` is equivalent to ``a != b``,

   ``gt(a, b)`` is equivalent to ``a > b`` and ``ge(a, b)`` is equivalent to ``a

   >= b``.  Note that unlike the built-in :func:`cmp`, these functions can

   return any value, which may or may not be interpretable as a Boolean value.

   See :ref:`comparisons` for more information about rich comparisons.

   .. versionadded:: 2.2

The logical operations are also generally applicable to all objects, and support

truth tests, identity tests, and boolean operations:

.. function:: not_(obj)

              __not__(obj)

   Return the outcome of :keyword:`not` *obj*.  (Note that there is no

   :meth:`__not__` method for object instances; only the interpreter core defines

   this operation.  The result is affected by the :meth:`__nonzero__` and

   :meth:`__len__` methods.)

.. function:: truth(obj)

   Return :const:`True` if *obj* is true, and :const:`False` otherwise.  This is

   equivalent to using the :class:`bool` constructor.

.. function:: is_(a, b)

   Return ``a is b``.  Tests object identity.

   .. versionadded:: 2.3

.. function:: is_not(a, b)

   Return ``a is not b``.  Tests object identity.

   .. versionadded:: 2.3

The mathematical and bitwise operations are the most numerous:

.. function:: abs(obj)

              __abs__(obj)

   Return the absolute value of *obj*.

.. function:: add(a, b)

              __add__(a, b)

   Return ``a + b``, for *a* and *b* numbers.

.. function:: and_(a, b)

              __and__(a, b)

   Return the bitwise and of *a* and *b*.

.. function:: div(a, b)

              __div__(a, b)

   Return ``a / b`` when ``__future__.division`` is not in effect.  This is

   also known as "classic" division.

.. function:: floordiv(a, b)

              __floordiv__(a, b)

   Return ``a // b``.

   .. versionadded:: 2.2

.. function:: inv(obj)

              invert(obj)

              __inv__(obj)

              __invert__(obj)

   Return the bitwise inverse of the number *obj*.  This is equivalent to ``~obj``.

   .. versionadded:: 2.0

      The names :func:`invert` and :func:`__invert__`.

.. function:: lshift(a, b)

              __lshift__(a, b)

   Return *a* shifted left by *b*.

.. function:: mod(a, b)

              __mod__(a, b)

   Return ``a % b``.

.. function:: mul(a, b)

              __mul__(a, b)

   Return ``a * b``, for *a* and *b* numbers.

.. function:: neg(obj)

              __neg__(obj)

   Return *obj* negated.

.. function:: or_(a, b)

              __or__(a, b)

   Return the bitwise or of *a* and *b*.

.. function:: pos(obj)

              __pos__(obj)

   Return *obj* positive.

.. function:: pow(a, b)

              __pow__(a, b)

   Return ``a ** b``, for *a* and *b* numbers.

   .. versionadded:: 2.3

.. function:: rshift(a, b)

              __rshift__(a, b)

   Return *a* shifted right by *b*.

.. function:: sub(a, b)

              __sub__(a, b)

   Return ``a - b``.

.. function:: truediv(a, b)

              __truediv__(a, b)

   Return ``a / b`` when ``__future__.division`` is in effect.  This is also

   known as "true" division.

   .. versionadded:: 2.2

.. function:: xor(a, b)

              __xor__(a, b)

   Return the bitwise exclusive or of *a* and *b*.

.. function:: index(a)

              __index__(a)

   Return *a* converted to an integer.  Equivalent to ``a.__index__()``.

   .. versionadded:: 2.5

Operations which work with sequences include:

.. function:: concat(a, b)

              __concat__(a, b)

   Return ``a + b`` for *a* and *b* sequences.

.. function:: contains(a, b)

              __contains__(a, b)

   Return the outcome of the test ``b in a``. Note the reversed operands.

   .. versionadded:: 2.0

      The name :func:`__contains__`.

.. function:: countOf(a, b)

   Return the number of occurrences of *b* in *a*.

.. function:: delitem(a, b)

              __delitem__(a, b)

   Remove the value of *a* at index *b*.

.. function:: delslice(a, b, c)

              __delslice__(a, b, c)

   Delete the slice of *a* from index *b* to index *c-1*.

.. function:: getitem(a, b)

              __getitem__(a, b)

   Return the value of *a* at index *b*.

.. function:: getslice(a, b, c)

              __getslice__(a, b, c)

   Return the slice of *a* from index *b* to index *c-1*.

.. function:: indexOf(a, b)

   Return the index of the first of occurrence of *b* in *a*.

.. function:: repeat(a, b)

              __repeat__(a, b)

   Return ``a * b`` where *a* is a sequence and *b* is an integer.

.. function:: sequenceIncludes(...)

   .. deprecated:: 2.0

      Use :func:`contains` instead.

   Alias for :func:`contains`.

.. function:: setitem(a, b, c)

              __setitem__(a, b, c)

   Set the value of *a* at index *b* to *c*.

.. function:: setslice(a, b, c, v)

              __setslice__(a, b, c, v)

   Set the slice of *a* from index *b* to index *c-1* to the sequence *v*.

Many operations have an "in-place" version.  The following functions provide a

more primitive access to in-place operators than the usual syntax does; for

example, the :term:`statement` ``x += y`` is equivalent to

``x = operator.iadd(x, y)``.  Another way to put it is to say that

``z = operator.iadd(x, y)`` is equivalent to the compound statement

``z = x; z += y``.

.. function:: iadd(a, b)

              __iadd__(a, b)

   ``a = iadd(a, b)`` is equivalent to ``a += b``.

   .. versionadded:: 2.5

.. function:: iand(a, b)

              __iand__(a, b)

   ``a = iand(a, b)`` is equivalent to ``a &= b``.

   .. versionadded:: 2.5

.. function:: iconcat(a, b)

              __iconcat__(a, b)

   ``a = iconcat(a, b)`` is equivalent to ``a += b`` for *a* and *b* sequences.

   .. versionadded:: 2.5

.. function:: idiv(a, b)

              __idiv__(a, b)

   ``a = idiv(a, b)`` is equivalent to ``a /= b`` when ``__future__.division`` is

   not in effect.

   .. versionadded:: 2.5

.. function:: ifloordiv(a, b)

              __ifloordiv__(a, b)

   ``a = ifloordiv(a, b)`` is equivalent to ``a //= b``.

   .. versionadded:: 2.5

.. function:: ilshift(a, b)

              __ilshift__(a, b)

   ``a = ilshift(a, b)`` is equivalent to ``a <``\ ``<= b``.

   .. versionadded:: 2.5

.. function:: imod(a, b)

              __imod__(a, b)

   ``a = imod(a, b)`` is equivalent to ``a %= b``.

   .. versionadded:: 2.5

.. function:: imul(a, b)

              __imul__(a, b)

   ``a = imul(a, b)`` is equivalent to ``a *= b``.

   .. versionadded:: 2.5

.. function:: ior(a, b)

              __ior__(a, b)

   ``a = ior(a, b)`` is equivalent to ``a |= b``.

   .. versionadded:: 2.5

.. function:: ipow(a, b)

              __ipow__(a, b)

   ``a = ipow(a, b)`` is equivalent to ``a **= b``.

   .. versionadded:: 2.5

.. function:: irepeat(a, b)

              __irepeat__(a, b)

   ``a = irepeat(a, b)`` is equivalent to ``a *= b`` where *a* is a sequence and

   *b* is an integer.

   .. versionadded:: 2.5

.. function:: irshift(a, b)

              __irshift__(a, b)

   ``a = irshift(a, b)`` is equivalent to ``a >>= b``.

   .. versionadded:: 2.5

.. function:: isub(a, b)

              __isub__(a, b)

   ``a = isub(a, b)`` is equivalent to ``a -= b``.

   .. versionadded:: 2.5

.. function:: itruediv(a, b)

              __itruediv__(a, b)

   ``a = itruediv(a, b)`` is equivalent to ``a /= b`` when ``__future__.division``

   is in effect.

   .. versionadded:: 2.5

.. function:: ixor(a, b)

              __ixor__(a, b)

   ``a = ixor(a, b)`` is equivalent to ``a ^= b``.

   .. versionadded:: 2.5

The :mod:`operator` module also defines a few predicates to test the type of

objects.

.. note::

   Be careful not to misinterpret the results of these functions; only

   :func:`isCallable` has any measure of reliability with instance objects.

   For example:

      >>> class C:

      ...     pass

      ... 

      >>> import operator

      >>> obj = C()

      >>> operator.isMappingType(obj)

      True

.. note::

   Python 3 is expected to introduce abstract base classes for

   collection types, so it should be possible to write, for example,

   ``isinstance(obj, collections.Mapping)`` and ``isinstance(obj,

   collections.Sequence)``.

.. function:: isCallable(obj)

   .. deprecated:: 2.0

      Use the :func:`callable` built-in function instead.

   Returns true if the object *obj* can be called like a function, otherwise it

   returns false.  True is returned for functions, bound and unbound methods, class

   objects, and instance objects which support the :meth:`__call__` method.

.. function:: isMappingType(obj)

   Returns true if the object *obj* supports the mapping interface. This is true for

   dictionaries and all instance objects defining :meth:`__getitem__`.

   .. warning::

      There is no reliable way to test if an instance supports the complete mapping

      protocol since the interface itself is ill-defined.  This makes this test less

      useful than it otherwise might be.

.. function:: isNumberType(obj)

   Returns true if the object *obj* represents a number.  This is true for all

   numeric types implemented in C.

   .. warning::

      There is no reliable way to test if an instance supports the complete numeric

      interface since the interface itself is ill-defined.  This makes this test less

      useful than it otherwise might be.

.. function:: isSequenceType(obj)

   Returns true if the object *obj* supports the sequence protocol. This returns true

   for all objects which define sequence methods in C, and for all instance objects

   defining :meth:`__getitem__`.

   .. warning::

      There is no reliable way to test if an instance supports the complete sequence

      interface since the interface itself is ill-defined.  This makes this test less

      useful than it otherwise might be.

Example: Build a dictionary that maps the ordinals from ``0`` to ``255`` to

their character equivalents.

   >>> d = {}

   >>> keys = range(256)

   >>> vals = map(chr, keys)

   >>> map(operator.setitem, [d]*len(keys), keys, vals)   # doctest: +SKIP

.. XXX: find a better, readable, example

The :mod:`operator` module also defines tools for generalized attribute and item

lookups.  These are useful for making fast field extractors as arguments for

:func:`map`, :func:`sorted`, :meth:`itertools.groupby`, or other functions that

expect a function argument.

.. function:: attrgetter(attr[, args...])

   Return a callable object that fetches *attr* from its operand. If more than one

   attribute is requested, returns a tuple of attributes. After,

   ``f = attrgetter('name')``, the call ``f(b)`` returns ``b.name``.  After,

   ``f = attrgetter('name', 'date')``, the call ``f(b)`` returns ``(b.name,

   b.date)``.

   The attribute names can also contain dots; after ``f = attrgetter('date.month')``,

   the call ``f(b)`` returns ``b.date.month``.

   .. versionadded:: 2.4

   .. versionchanged:: 2.5

      Added support for multiple attributes.

   .. versionchanged:: 2.6

      Added support for dotted attributes.

.. function:: itemgetter(item[, args...])

   Return a callable object that fetches *item* from its operand using the

   operand's :meth:`__getitem__` method.  If multiple items are specified,

   returns a tuple of lookup values.  Equivalent to::

        def itemgetter(*items):

            if len(items) == 1: