#!/usr/bin/env python
     # encoding: utf-8
     #
     # Copyright (c) 2010 Doug Hellmann.  All rights reserved.
     #
     """Look behind assertion.
     """
     #end_pymotw_header
     
     import re
     
     twitter = re.compile(
         '''
         # A twitter handle: @username
         (?<=@)
         ([\w\d_]+)       # username
         ''',
         re.UNICODE | re.VERBOSE)
     
     text = '''This text includes two Twitter handles.
     One for @ThePSF, and one for the author, @doughellmann.
     '''
     
     print text
     for match in twitter.findall(text):
         print 'Handle:', match