The operator module

This module provides a “functional” interface to the standard operators in Python. The functions in this module can be used instead of some lambda constructs, when processing data with functions like map and filter.

They are also quite popular among people who like to write obscure code, for obvious reasons.

Example: Using the operator module

# File: operator-example-1.py

import operator

sequence = 1, 2, 4

print "add", "=>", reduce(operator.add, sequence)
print "sub", "=>", reduce(operator.sub, sequence)
print "mul", "=>", reduce(operator.mul, sequence)
print "concat", "=>", operator.concat("spam", "egg")
print "repeat", "=>", operator.repeat("spam", 5)
print "getitem", "=>", operator.getitem(sequence, 2)
print "indexOf", "=>", operator.indexOf(sequence, 2)
print "sequenceIncludes", "=>", operator.sequenceIncludes(sequence, 3)

add => 7
sub => -5
mul => 8
concat => spamegg
repeat => spamspamspamspamspam
getitem => 4
indexOf => 1
sequenceIncludes => 0

The module also contains a few functions which can be used to check object types:

Example: Using the operator module for type checking

# File: operator-example-2.py

import operator
import UserList

def dump(data):
    print type(data), "=>",
    if operator.isCallable(data):
        print "CALLABLE",
    if operator.isMappingType(data):
        print "MAPPING",
    if operator.isNumberType(data):
        print "NUMBER",
    if operator.isSequenceType(data):
        print "SEQUENCE",
    print
        
dump(0)
dump("string")
dump("string"[0])
dump([1, 2, 3])
dump((1, 2, 3))
dump({"a": 1})
dump(len) # function
dump(UserList) # module
dump(UserList.UserList) # class
dump(UserList.UserList()) # instance

<type 'int'> => NUMBER
<type 'string'> => SEQUENCE
<type 'string'> => SEQUENCE
<type 'list'> => SEQUENCE
<type 'tuple'> => SEQUENCE
<type 'dictionary'> => MAPPING
<type 'builtin_function_or_method'> => CALLABLE
<type 'module'> =>
<type 'class'> => CALLABLE
<type 'instance'> => MAPPING NUMBER SEQUENCE

Note that the operator module doesn’t handle object instances in a sane fashion. In other words, be careful when you use the isNumberType, isMappingType, and isSequenceType functions. It’s easy to make your code less flexible than it has to be.

Also note that a string sequence member (a character) is also a sequence. If you’re writing a recursive function that uses isSequenceType to traverse an object tree, you better not pass it an ordinary string (or anything containing one).