The operator Module

The operator 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. The operator module is demonstrated in Example 1-62.

Example 1-62. 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

Example 1-63 shows some operator functions that can be used to check object types.

Example 1-63. 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 => NUMBER => SEQUENCE => SEQUENCE => SEQUENCE => SEQUENCE => MAPPING => CALLABLE => => CALLABLE => MAPPING NUMBER SEQUENCE

Note that the operator module doesn't handle object instances in a normal fashion. 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).