Back reference por nombre

[rrc@Pridd ~]$ python3
Python 3.4.3 (default, Jul  1 2015, 18:38:11) 
[GCC 4.9.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> s = "Sun Oct 14 13:47:03 CEST 2012"
>>> expr = r"\b(?P<hours>\d\d):(?P<minutes>\d\d):(?P<seconds>\d\d)\b"
>>> x = re.search(expr,s)
>>> x.group('hours')
'13'
>>> x.group('minutes')
'47'
>>> x.start('minutes')
14
>>> x.end('minutes')
16
>>> x.span('seconds')
(17, 19)
>>>