Here is an example of a failed match where None is returned: : match « Regular Expressions « Python Tutorial

import re

m = re.match('foo', 'bar')# pattern does not match string
if m is not None: m.group()# (1-line version of ifclause)

m = re.match('foo', 'food on the table') # match succeeds
print m.group()

print re.match('foo', 'food on the table').group()

16.4.match
	16.4.1.	Matching Strings with match()
	16.4.2.	Here is an example of a failed match where None is returned:
	16.4.3.	Repetition, Special Characters, and Grouping
	16.4.4.	Compiled regular-expression and match objects.
	16.4.5.	Repetition patterns, matching vs searching.
	16.4.6.	classes and special sequences.
	16.4.7.	Dig out path