>>> s = 'foobar'
>>> m = re.compile('foo(bar)').search(s)
>>> m
<_sre.SRE_Match object at 0x688a0>
>>> if m.group(1) != None:
...  print m.group(1)
... 
bar
>>> if m.group(3) != None:
...  print m.group(3)
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: no such group