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

.. module:: operator

:synopsis: Functions corresponding to the standard operators.

**Source code:** :source:`Lib/operator.py`

.. testsetup::

import operator

from operator import itemgetter, iadd

The :mod:`!operator` module exports a set of efficient functions corresponding to

the intrinsic operators of Python. For example, ``operator.add(x, y)`` is

equivalent to the expression ``x+y``. Many function names are those used for

special methods, without the double underscores. For backward compatibility,

many of these have a variant with the double underscores kept. The variants

without the double underscores are preferred for clarity.

The functions fall into categories that perform object comparisons, logical

operations, mathematical operations and sequence operations.

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 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.

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:`~object.__bool__` and

:meth:`~object.__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.

.. function:: is_not(a, b)

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

.. function:: is_none(a)

Return ``a is None``. Tests object identity.

.. versionadded:: 3.14

.. function:: is_not_none(a)

Return ``a is not None``. Tests object identity.

.. versionadded:: 3.14

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 ``a & b``.

.. function:: floordiv(a, b)

__floordiv__(a, b)

Return ``a // b``.

.. function:: index(a)

__index__(a)

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

.. versionchanged:: 3.10

The result always has exact type :class:`int`. Previously, the result

could have been an instance of a subclass of ``int``.

.. function:: inv(obj)

invert(obj)

__inv__(obj)

__invert__(obj)

Return ``~obj``.

.. function:: lshift(a, b)

__lshift__(a, b)

Return ``a << b``.

.. function:: mod(a, b)

__mod__(a, b)

Return ``a % b``.

.. function:: mul(a, b)

__mul__(a, b)

Return ``a * b``.

.. function:: matmul(a, b)

__matmul__(a, b)

Return ``a @ b``.

.. versionadded:: 3.5

.. function:: neg(obj)

__neg__(obj)

Return *obj* negated (``-obj``).

.. function:: or_(a, b)

__or__(a, b)

Return ``a | b``.

.. function:: pos(obj)

__pos__(obj)

Return ``+obj``.

.. function:: pow(a, b)

__pow__(a, b)

Return ``a ** b``.

.. function:: rshift(a, b)

__rshift__(a, b)

Return ``a >> b``.

.. function:: sub(a, b)

__sub__(a, b)

Return ``a - b``.

.. function:: truediv(a, b)

__truediv__(a, b)

Return ``a / b`` where 2/3 is .66 rather than 0. This is also known as

"true" division.

.. function:: xor(a, b)

__xor__(a, b)

Return ``a ^ b``.

Operations which work with sequences (some of them with mappings too) 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.

.. 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:: getitem(a, b)

__getitem__(a, b)

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

.. function:: indexOf(a, b)

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

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

__setitem__(a, b, c)

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

.. function:: length_hint(obj, default=0)

Return an estimated length for the object *obj*. First try to return its

actual length, then an estimate using :meth:`object.__length_hint__`, and

finally return the default value.

.. versionadded:: 3.4

The following operation works with callables:

.. function:: call(obj, /, *args, **kwargs)

__call__(obj, /, *args, **kwargs)

Return ``obj(*args, **kwargs)``.

.. versionadded:: 3.11

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)

attrgetter(*attrs)

Return a callable object that fetches *attr* from its operand.

If more than one attribute is requested, returns a tuple of attributes.

The attribute names can also contain dots. For example:

* 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)``.

* After ``f = attrgetter('name.first', 'name.last')``, the call ``f(b)``

returns ``(b.name.first, b.name.last)``.

Equivalent to::

.. function:: itemgetter(item)

itemgetter(*items)

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

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

returns a tuple of lookup values. For example:

* After ``f = itemgetter(2)``, the call ``f(r)`` returns ``r[2]``.

* After ``g = itemgetter(2, 5, 3)``, the call ``g(r)`` returns

``(r[2], r[5], r[3])``.

Equivalent to::

The items can be any type accepted by the operand's :meth:`~object.__getitem__`

method. Dictionaries accept any :term:`hashable` value. Lists, tuples, and

strings accept an index or a slice:

>>> itemgetter(1)('ABCDEFG')

'B'

>>> itemgetter(1, 3, 5)('ABCDEFG')

('B', 'D', 'F')

>>> itemgetter(slice(2, None))('ABCDEFG')

'CDEFG'

>>> soldier = dict(rank='captain', name='dotterbart')

>>> itemgetter('rank')(soldier)

'captain'

Example of using :func:`itemgetter` to retrieve specific fields from a

tuple record:

>>> inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)]

>>> getcount = itemgetter(1)

>>> list(map(getcount, inventory))

[3, 2, 5, 1]

>>> sorted(inventory, key=getcount)

[('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)]

.. function:: methodcaller(name, /, *args, **kwargs)

Return a callable object that calls the method *name* on its operand. If

additional arguments and/or keyword arguments are given, they will be given

to the method as well. For example:

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

* After ``f = methodcaller('name', 'foo', bar=1)``, the call ``f(b)``

returns ``b.name('foo', bar=1)``.

Equivalent to::

.. _operator-map:

Mapping Operators to Functions

This table shows how abstract operations correspond to operator symbols in the

Python syntax and the functions in the :mod:`!operator` module.

| Operation | Syntax | Function |

| Addition | ``a + b`` | ``add(a, b)`` |

| Concatenation | ``seq1 + seq2`` | ``concat(seq1, seq2)`` |

| Containment Test | ``obj in seq`` | ``contains(seq, obj)`` |

| Division | ``a / b`` | ``truediv(a, b)`` |

| Division | ``a // b`` | ``floordiv(a, b)`` |

| Bitwise And, or | ``a & b`` | ``and_(a, b)`` |

| Intersection | | |

| Bitwise Exclusive Or, | ``a ^ b`` | ``xor(a, b)`` |

| or Symmetric | | |

| Difference | | |

| Bitwise Inversion, or | ``~ a`` | ``invert(a)`` |

| Complement | | |

| Bitwise Or, or | ``a | b`` | ``or_(a, b)`` |

| Union | | |

| Exponentiation | ``a ** b`` | ``pow(a, b)`` |

| Identity | ``a is b`` | ``is_(a, b)`` |

| Identity | ``a is not b`` | ``is_not(a, b)`` |

| Identity | ``a is None`` | ``is_none(a)`` |

| Identity | ``a is not None`` | ``is_not_none(a)`` |

| Indexed Assignment | ``obj[k] = v`` | ``setitem(obj, k, v)`` |

| Indexed Deletion | ``del obj[k]`` | ``delitem(obj, k)`` |

| Indexing | ``obj[k]`` | ``getitem(obj, k)`` |

| Left Shift | ``a << b`` | ``lshift(a, b)`` |

| Modulo | ``a % b`` | ``mod(a, b)`` |

| Multiplication | ``a * b`` | ``mul(a, b)`` |

| Matrix Multiplication | ``a @ b`` | ``matmul(a, b)`` |

| Negation (Arithmetic) | ``- a`` | ``neg(a)`` |

| Negation (Logical) | ``not a`` | ``not_(a)`` |

| Positive | ``+ a`` | ``pos(a)`` |

| Right Shift | ``a >> b`` | ``rshift(a, b)`` |

| Slice Assignment | ``seq[i:j] = values`` | ``setitem(seq, slice(i, j), values)`` |

| Slice Deletion | ``del seq[i:j]`` | ``delitem(seq, slice(i, j))`` |

| Slicing | ``seq[i:j]`` | ``getitem(seq, slice(i, j))`` |

| String Formatting | ``s % obj`` | ``mod(s, obj)`` |

| Subtraction | ``a - b`` | ``sub(a, b)`` |

| Truth Test | ``obj`` | ``truth(obj)`` |

| Ordering | ``a < b`` | ``lt(a, b)`` |

| Ordering | ``a <= b`` | ``le(a, b)`` |

| Equality | ``a == b`` | ``eq(a, b)`` |

| Difference | ``a != b`` | ``ne(a, b)`` |

| Ordering | ``a >= b`` | ``ge(a, b)`` |

| Ordering | ``a > b`` | ``gt(a, b)`` |

In-place Operators

Many operations have an "in-place" version. Listed below are functions

providing 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``.

In those examples, note that when an in-place method is called, the computation

and assignment are performed in two separate steps. The in-place functions

listed below only do the first step, calling the in-place method. The second

step, assignment, is not handled.

For immutable targets such as strings, numbers, and tuples, the updated

value is computed, but not assigned back to the input variable:

>>> a = 'hello'

>>> iadd(a, ' world')

>>> a

For mutable targets such as lists and dictionaries, the in-place method

will perform the update, so no subsequent assignment is necessary:

>>> s = ['h', 'e', 'l', 'l', 'o']

>>> iadd(s, [' ', 'w', 'o', 'r', 'l', 'd'])

>>> s

.. function:: iadd(a, b)

__iadd__(a, b)

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

.. function:: iand(a, b)

__iand__(a, b)

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

.. function:: iconcat(a, b)

__iconcat__(a, b)

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

.. function:: ifloordiv(a, b)

__ifloordiv__(a, b)

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

.. function:: ilshift(a, b)

__ilshift__(a, b)

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

.. function:: imod(a, b)

__imod__(a, b)

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

.. function:: imul(a, b)

__imul__(a, b)

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

.. function:: imatmul(a, b)

__imatmul__(a, b)

``a = imatmul(a, b)`` is equivalent to ``a @= b``.

.. versionadded:: 3.5

.. function:: ior(a, b)

__ior__(a, b)

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

.. function:: ipow(a, b)

__ipow__(a, b)

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

.. function:: irshift(a, b)

__irshift__(a, b)

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

.. function:: isub(a, b)

__isub__(a, b)

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

.. function:: itruediv(a, b)

__itruediv__(a, b)

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

.. function:: ixor(a, b)

__ixor__(a, b)

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