9.9. operator — Standard operators as functions
The 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, 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:
-
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 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 cmp(), 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 __nonzero__() and
__len__() methods.)
-
operator.truth(obj)
Return True if obj is true, and False otherwise. This is
equivalent to using the bool 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.abs(obj)
-
operator.__abs__(obj)
Return the absolute value of obj.
-
operator.add(a, b)
-
operator.__add__(a, b)
Return a + b, for a and b numbers.
-
operator.and_(a, b)
-
operator.__and__(a, b)
Return the bitwise and of a and b.
-
operator.div(a, b)
-
operator.__div__(a, b)
Return a / b when __future__.division is not in effect. This is
also known as “classic” division.
-
operator.floordiv(a, b)
-
operator.__floordiv__(a, b)
Return a // b.
-
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.lshift(a, b)
-
operator.__lshift__(a, b)
Return a shifted left by b.
-
operator.mod(a, b)
-
operator.__mod__(a, b)
Return a % b.
-
operator.mul(a, b)
-
operator.__mul__(a, b)
Return a * b, for a and b numbers.
-
operator.neg(obj)
-
operator.__neg__(obj)
Return obj negated (-obj).
-
operator.or_(a, b)
-
operator.__or__(a, b)
Return the bitwise or of a and b.
-
operator.pos(obj)
-
operator.__pos__(obj)
Return obj positive (+obj).
-
operator.pow(a, b)
-
operator.__pow__(a, b)
Return a ** b, for a and b numbers.
-
operator.rshift(a, b)
-
operator.__rshift__(a, b)
Return a shifted right by b.
-
operator.sub(a, b)
-
operator.__sub__(a, b)
Return a - b.
-
operator.truediv(a, b)
-
operator.__truediv__(a, b)
Return a / b when __future__.division is in effect. This is also
known as “true” division.
-
operator.xor(a, b)
-
operator.__xor__(a, b)
Return the bitwise exclusive or of a and b.
Operations which work with sequences (some of them with mappings too) include:
-
operator.concat(a, b)
-
operator.__concat__(a, b)
Return a + b for a and b sequences.
-
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.delitem(a, b)
-
operator.__delitem__(a, b)
Remove the value of a at index b.
-
operator.delslice(a, b, c)
-
operator.__delslice__(a, b, c)
Delete the slice of a from index b to index c-1.
Deprecated since version 2.6: This function is removed in Python 3.x. Use delitem() with a slice
index.
-
operator.getitem(a, b)
-
operator.__getitem__(a, b)
Return the value of a at index b.
-
operator.getslice(a, b, c)
-
operator.__getslice__(a, b, c)
Return the slice of a from index b to index c-1.
Deprecated since version 2.6: This function is removed in Python 3.x. Use getitem() with a slice
index.
-
operator.indexOf(a, b)
Return the index of the first of occurrence of b in a.
-
operator.repeat(a, b)
-
operator.__repeat__(a, b)
Deprecated since version 2.7: Use __mul__() instead.
Return a * b where a is a sequence and b is an integer.
-
operator.sequenceIncludes(...)
Deprecated since version 2.0: Use contains() instead.
Alias for contains().
-
operator.setitem(a, b, c)
-
operator.__setitem__(a, b, c)
Set the value of a at index b to c.
-
operator.setslice(a, b, c, v)
-
operator.__setslice__(a, b, c, v)
Set the slice of a from index b to index c-1 to the sequence v.
Deprecated since version 2.6: This function is removed in Python 3.x. Use setitem() with a slice
index.
Example use of operator functions:
>>> # Elementwise multiplication
>>> map(mul, [0, 1, 2, 3], [10, 20, 30, 40])
[0, 20, 60, 120]
>>> # Dot product
>>> sum(map(mul, [0, 1, 2, 3], [10, 20, 30, 40]))
200
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 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.
-
operator.iadd(a, b)
-
operator.__iadd__(a, b)
a = iadd(a, b) is equivalent to a += b.
-
operator.iand(a, b)
-
operator.__iand__(a, b)
a = iand(a, b) is equivalent to a &= b.
-
operator.iconcat(a, b)
-
operator.__iconcat__(a, b)
a = iconcat(a, b) is equivalent to a += b for a and b sequences.
-
operator.idiv(a, b)
-
operator.__idiv__(a, b)
a = idiv(a, b) is equivalent to a /= b when __future__.division is
not in effect.
-
operator.ifloordiv(a, b)
-
operator.__ifloordiv__(a, b)
a = ifloordiv(a, b) is equivalent to a //= b.
-
operator.ilshift(a, b)
-
operator.__ilshift__(a, b)
a = ilshift(a, b) is equivalent to a <<= b.
-
operator.imod(a, b)
-
operator.__imod__(a, b)
a = imod(a, b) is equivalent to a %= b.
-
operator.imul(a, b)
-
operator.__imul__(a, b)
a = imul(a, b) is equivalent to a *= b.
-
operator.ior(a, b)
-
operator.__ior__(a, b)
a = ior(a, b) is equivalent to a |= b.
-
operator.ipow(a, b)
-
operator.__ipow__(a, b)
a = ipow(a, b) is equivalent to a **= b.
-
operator.irepeat(a, b)
-
operator.__irepeat__(a, b)
Deprecated since version 2.7: Use __imul__() instead.
a = irepeat(a, b) is equivalent to a *= b where a is a sequence and
b is an integer.
-
operator.irshift(a, b)
-
operator.__irshift__(a, b)
a = irshift(a, b) is equivalent to a >>= b.
-
operator.isub(a, b)
-
operator.__isub__(a, b)
a = isub(a, b) is equivalent to a -= b.
-
operator.itruediv(a, b)
-
operator.__itruediv__(a, b)
a = itruediv(a, b) is equivalent to a /= b when __future__.division
is in effect.
-
operator.ixor(a, b)
-
operator.__ixor__(a, b)
a = ixor(a, b) is equivalent to a ^= b.
The operator module also defines a few predicates to test the type of
objects; however, these are not all reliable. It is preferable to test
abstract base classes instead (see collections and
numbers for details).
-
operator.isCallable(obj)
Deprecated since version 2.0: Use isinstance(x, collections.Callable) 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 __call__() method.
-
operator.isMappingType(obj)
Deprecated since version 2.7: Use isinstance(x, collections.Mapping) instead.
Returns true if the object obj supports the mapping interface. This is true for
dictionaries and all instance objects defining __getitem__().
-
operator.isNumberType(obj)
Deprecated since version 2.7: Use isinstance(x, numbers.Number) instead.
Returns true if the object obj represents a number. This is true for all
numeric types implemented in C.
-
operator.isSequenceType(obj)
Deprecated since version 2.7: Use isinstance(x, collections.Sequence) instead.
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 __getitem__().
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)
-
operator.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:
def attrgetter(*items):
if len(items) == 1:
attr = items[0]
def g(obj):
return resolve_attr(obj, attr)
else:
def g(obj):
return tuple(resolve_attr(obj, attr) for attr in items)
return g
def resolve_attr(obj, attr):
for name in attr.split("."):
obj = getattr(obj, name)
return obj
Changed in version 2.5: Added support for multiple attributes.
Changed in version 2.6: Added support for dotted attributes.
-
operator.itemgetter(item)
-
operator.itemgetter(*items)
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. 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:
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'
Changed in version 2.5: Added support for multiple item extraction.
Example of using itemgetter() to retrieve specific fields from a
tuple record:
>>> inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)]
>>> getcount = itemgetter(1)
>>> 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. 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:
def methodcaller(name, *args, **kwargs):
def caller(obj):
return getattr(obj, name)(*args, **kwargs)
return caller
9.9.1. 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) (without
__future__.division) |
| Division |
a / b |
truediv(a, b) (with
__future__.division) |
| 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) |