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.

New in version 2.2.

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.

New in version 2.3.

operator.is_not(a, b)

Return a is not b. Tests object identity.

New in version 2.3.

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.

New in version 2.2.

operator.index(a)
operator.__index__(a)

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

New in version 2.5.

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.

New in version 2.0: The names invert() and __invert__().

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.

New in version 2.3.

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.

New in version 2.2.

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.

New in version 2.0: The name __contains__().

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.

New in version 2.5.

operator.iand(a, b)
operator.__iand__(a, b)

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

New in version 2.5.

operator.iconcat(a, b)
operator.__iconcat__(a, b)

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

New in version 2.5.

operator.idiv(a, b)
operator.__idiv__(a, b)

a = idiv(a, b) is equivalent to a /= b when __future__.division is not in effect.

New in version 2.5.

operator.ifloordiv(a, b)
operator.__ifloordiv__(a, b)

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

New in version 2.5.

operator.ilshift(a, b)
operator.__ilshift__(a, b)

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

New in version 2.5.

operator.imod(a, b)
operator.__imod__(a, b)

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

New in version 2.5.

operator.imul(a, b)
operator.__imul__(a, b)

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

New in version 2.5.

operator.ior(a, b)
operator.__ior__(a, b)

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

New in version 2.5.

operator.ipow(a, b)
operator.__ipow__(a, b)

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

New in version 2.5.

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.

New in version 2.5.

operator.irshift(a, b)
operator.__irshift__(a, b)

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

New in version 2.5.

operator.isub(a, b)
operator.__isub__(a, b)

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

New in version 2.5.

operator.itruediv(a, b)
operator.__itruediv__(a, b)

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

New in version 2.5.

operator.ixor(a, b)
operator.__ixor__(a, b)

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

New in version 2.5.

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

New in version 2.4.

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'

New in version 2.4.

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

New in version 2.6.

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)