6.7 operator -- Standard operators as functions.

6.7 `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, 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:

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 unlike the built-in cmp(), these functions can return any value, which may or may not be interpretable as a Boolean value. See the Python Reference Manual 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:

not_( o)
__not__( o): Return the outcome of not o. (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.)

truth( o): Return True if o is true, and False otherwise. This is equivalent to using the bool constructor.

is_( a, b): Return a is b. Tests object identity. New in version 2.3.

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:

abs( o)
__abs__( o): Return the absolute value of o.

add( a, b)
__add__( a, b): Return a + b, for a and b numbers.

and_( a, b)
__and__( a, b): Return the bitwise and of a and b.

div( a, b)
__div__( a, b): Return a / b when __future__.division is not in effect. This is also known as ``classic'' division.

floordiv( a, b)
__floordiv__( a, b): Return a // b. New in version 2.2.

inv( o)
invert( o)
__inv__( o)
__invert__( o): Return the bitwise inverse of the number o. This is equivalent to ~o. The names invert() and __invert__() were added in Python 2.0.

lshift( a, b)
__lshift__( a, b): Return a shifted left by b.

mod( a, b)
__mod__( a, b): Return a % b.

mul( a, b)
__mul__( a, b): Return a * b, for a and b numbers.

neg( o)
__neg__( o): Return o negated.

or_( a, b)
__or__( a, b): Return the bitwise or of a and b.

pos( o)
__pos__( o): Return o positive.

pow( a, b)
__pow__( a, b): Return a ** b, for a and b numbers. New in version 2.3.

rshift( a, b)
__rshift__( a, b): Return a shifted right by b.

sub( a, b)
__sub__( a, b): Return a - b.

truediv( a, b)
__truediv__( a, b): Return a / b when __future__.division is in effect. This is also known as ``true'' division. New in version 2.2.

xor( a, b)
__xor__( a, b): Return the bitwise exclusive or of a and b.

index( a)
__index__( a): Return a converted to an integer. Equivalent to a.__index__(). New in version 2.5.

Operations which work with sequences include:

concat( a, b)
__concat__( a, b): Return a + b for a and b sequences.

contains( a, b)
__contains__( a, b): Return the outcome of the test b in a. Note the reversed operands. The name __contains__() was added in Python 2.0.

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

delitem( a, b)
__delitem__( a, b): Remove the value of a at index b.

delslice( a, b, c)
__delslice__( a, b, c): Delete the slice of a from index b to index c-1.

getitem( a, b)
__getitem__( a, b): Return the value of a at index b.

getslice( a, b, c)
__getslice__( a, b, c): Return the slice of a from index b to index c-1.

indexOf( a, b): Return the index of the first of occurrence of b in a.

repeat( a, b)
__repeat__( a, b): Return a * b where a is a sequence and b is an integer.

sequenceIncludes( ...): Deprecated since release 2.0. Use contains() instead.
Alias for contains().

setitem( a, b, c)
__setitem__( a, b, c): Set the value of a at index b to c.

setslice( a, b, c, v)
__setslice__( a, b, c, v): Set the slice of a from index b to index c-1 to the sequence v.

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.

iadd( a, b)
__iadd__( a, b): a = iadd(a, b) is equivalent to a += b. New in version 2.5.

iand( a, b)
__iand__( a, b): a = iand(a, b) is equivalent to a &= b. New in version 2.5.

iconcat( a, b)
__iconcat__( a, b): a = iconcat(a, b) is equivalent to a += b for a and b sequences. New in version 2.5.

idiv( a, b)
__idiv__( a, b): a = idiv(a, b) is equivalent to a /= b when __future__.division is not in effect. New in version 2.5.

ifloordiv( a, b)
__ifloordiv__( a, b): a = ifloordiv(a, b) is equivalent to a //= b. New in version 2.5.

ilshift( a, b)
__ilshift__( a, b): a = ilshift(a, b) is equivalent to a <<= b. New in version 2.5.

imod( a, b)
__imod__( a, b): a = imod(a, b) is equivalent to a %= b. New in version 2.5.

imul( a, b)
__imul__( a, b): a = imul(a, b) is equivalent to a *= b. New in version 2.5.

ior( a, b)
__ior__( a, b): a = ior(a, b) is equivalent to a |= b. New in version 2.5.

ipow( a, b)
__ipow__( a, b): a = ipow(a, b) is equivalent to a **= b. New in version 2.5.

irepeat( a, b)
__irepeat__( a, b): a = irepeat(a, b) is equivalent to a *= b where a is a sequence and b is an integer. New in version 2.5.

irshift( a, b)
__irshift__( a, b): a = irshift(a, b) is equivalent to a >>= b. New in version 2.5.

isub( a, b)
__isub__( a, b): a = isub(a, b) is equivalent to a -= b. New in version 2.5.

itruediv( a, b)
__itruediv__( a, b): a = itruediv(a, b) is equivalent to a /= b when __future__.division is in effect. New in version 2.5.

ixor( a, b)
__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. Note: Be careful not to misinterpret the results of these functions; only isCallable() has any measure of reliability with instance objects. For example:

>>> class C:
...     pass
... 
>>> import operator
>>> o = C()
>>> operator.isMappingType(o)
True

isCallable( o): Deprecated since release 2.0. Use the callable() built-in function instead.
Returns true if the object o 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.

isMappingType( o): Returns true if the object o supports the mapping interface. This is true for dictionaries and all instance objects defining __getitem__. Warning: There is no reliable way to test if an instance supports the complete mapping protocol since the interface itself is ill-defined. This makes this test less useful than it otherwise might be.

isNumberType( o): Returns true if the object o represents a number. This is true for all numeric types implemented in C. Warning: There is no reliable way to test if an instance supports the complete numeric interface since the interface itself is ill-defined. This makes this test less useful than it otherwise might be.

isSequenceType( o): Returns true if the object o supports the sequence protocol. This returns true for all objects which define sequence methods in C, and for all instance objects defining __getitem__. Warning: There is no reliable way to test if an instance supports the complete sequence interface since the interface itself is ill-defined. This makes this test less useful than it otherwise might be.

Example: Build a dictionary that maps the ordinals from 0 to 255 to their character equivalents.

>>> import operator
>>> 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.

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 call "f(b)" returns "b.name". After, "f=attrgetter('name', 'date')", the call "f(b)" returns "(b.name, b.date)". New in version 2.4. Changed in version 2.5: Added support for multiple attributes.

itemgetter( item[, args...]): Return a callable object that fetches item from its operand. If more than one item is requested, returns a tuple of items. After, "f=itemgetter(2)", the call "f(b)" returns "b[2]". After, "f=itemgetter(2,5,3)", the call "f(b)" returns "(b[2], b[5], b[3])". New in version 2.4. Changed in version 2.5: Added support for multiple item extraction.

Examples:

>>> from operator import itemgetter
>>> 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)]

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