9.3. operator
— Standard operators as functions¶
The 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 and sequence operations.
The object comparison functions are useful for all objects, and are named after the rich comparison operators they support:

operator.
lt
(a, b)¶ 
operator.
le
(a, b)¶ 
operator.
eq
(a, b)¶ 
operator.
ne
(a, b)¶ 
operator.
ge
(a, b)¶ 
operator.
gt
(a, b)¶ 
operator.
__lt__
(a, b)¶ 
operator.
__le__
(a, b)¶ 
operator.
__eq__
(a, b)¶ 
operator.
__ne__
(a, b)¶ 
operator.
__ge__
(a, b)¶ 
operator.
__gt__
(a, b)¶ Perform “rich comparisons” between a and b. Specifically,
lt(a, b)
is equivalent toa < b
,le(a, b)
is equivalent toa <= b
,eq(a, b)
is equivalent toa == b
,ne(a, b)
is equivalent toa != b
,gt(a, b)
is equivalent toa > b
andge(a, b)
is equivalent toa >= b
. Note that these functions can return any value, which may or may not be interpretable as a Boolean value. See 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:

operator.
not_
(obj)¶ 
operator.
__not__
(obj)¶ Return the outcome of
not
obj. (Note that there is no__not__()
method for object instances; only the interpreter core defines this operation. The result is affected by the__bool__()
and__len__()
methods.)

operator.
truth
(obj)¶ Return
True
if obj is true, andFalse
otherwise. This is equivalent to using thebool
constructor.

operator.
is_
(a, b)¶ Return
a is b
. Tests object identity.

operator.
is_not
(a, b)¶ Return
a is not b
. Tests object identity.
The mathematical and bitwise operations are the most numerous:

operator.
index
(a)¶ 
operator.
__index__
(a)¶ Return a converted to an integer. Equivalent to
a.__index__()
.

operator.
inv
(obj)¶ 
operator.
invert
(obj)¶ 
operator.
__inv__
(obj)¶ 
operator.
__invert__
(obj)¶ Return the bitwise inverse of the number obj. This is equivalent to
~obj
.

operator.
truediv
(a, b)¶ 
operator.
__truediv__
(a, b)¶ Return
a / b
where 2/3 is .66 rather than 0. This is also known as “true” division.
Operations which work with sequences (some of them with mappings too) include:

operator.
contains
(a, b)¶ 
operator.
__contains__
(a, b)¶ Return the outcome of the test
b in a
. Note the reversed operands.

operator.
countOf
(a, b)¶ Return the number of occurrences of b in a.

operator.
indexOf
(a, b)¶ Return the index of the first of occurrence of b in a.
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)
The operator
module also defines tools for generalized attribute and item
lookups. These are useful for making fast field extractors as arguments for
map()
, sorted()
, itertools.groupby()
, or other functions that
expect a function argument.

operator.
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 callf(b)
returnsb.name
. After,f = attrgetter('name', 'date')
, the callf(b)
returns(b.name, b.date)
. Equivalent to:def attrgetter(*items): if any(not isinstance(item, str) for item in items): raise TypeError('attribute name must be a string') if len(items) == 1: attr = items[0] def g(obj): return resolve_attr(obj, attr) else: def g(obj): return tuple(resolve_att(obj, attr) for attr in items) return g def resolve_attr(obj, attr): for name in attr.split("."): obj = getattr(obj, name) return obj
The attribute names can also contain dots; after
f = attrgetter('date.month')
, the callf(b)
returnsb.date.month
.

operator.
itemgetter
(item[, args...])¶ Return a callable object that fetches item from its operand using the operand’s
__getitem__()
method. If multiple items are specified, returns a tuple of lookup values. Equivalent to:def itemgetter(*items): if len(items) == 1: item = items[0] def g(obj): return obj[item] else: def g(obj): return tuple(obj[item] for item in items) return g
The items can be any type accepted by the operand’s
__getitem__()
method. Dictionaries accept any 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'
Example of using
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)]

operator.
methodcaller
(name[, args...])¶ 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. After
f = methodcaller('name')
, the callf(b)
returnsb.name()
. Afterf = methodcaller('name', 'foo', bar=1)
, the callf(b)
returnsb.name('foo', bar=1)
. Equivalent to:def methodcaller(name, *args, **kwargs): def caller(obj): return getattr(obj, name)(*args, **kwargs) return caller
9.3.1. Mapping Operators to Functions¶
This table shows how abstract operations correspond to operator symbols in the
Python syntax and the functions in the 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 
div(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) 
Sequence Repetition  seq * i 
repeat(seq, i) 
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) 
9.4. Inplace Operators¶
Many operations have an “inplace” version. Listed below are functions
providing a more primitive access to inplace operators than the usual syntax
does; for example, the 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 inplace method is called, the computation and assignment are performed in two separate steps. The inplace functions listed below only do the first step, calling the inplace 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']

operator.
iconcat
(a, b)¶ 
operator.
__iconcat__
(a, b)¶ a = iconcat(a, b)
is equivalent toa += b
for a and b sequences.