# Source

# cpython / Doc / library / operator.rst

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

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`. 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 and sequence operations.

The object comparison functions are useful for all objects, and are named after the rich comparison operators they support:

The logical operations are also generally applicable to all objects, and support truth tests, identity tests, and boolean operations:

The mathematical and bitwise operations are the most numerous:

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

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

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.

## 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 | a & b |
and_(a, b) |

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

Bitwise Inversion | ~ a |
invert(a) |

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

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

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

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

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) |

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) |

## Inplace 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') 'hello world' >>> a 'hello'

For mutable targets such as lists and dictionaries, the inplace method will perform the update, so no subsequent assignment is necessary:

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