import re
p = re.compile('^(https?:\/\/)?([\w]+)\.([\w]+)+\.([a-z]{2,6}\.?)\/([\w-]+)*/([\w-]+)\.(gif|png|jpg)$')
p = re.finditer('^(https?:\/\/)?([\w]+)\.([\w]+)+\.([a-z]{2,6}\.?)\/([\w-]+)*/([\w-]+)\.(gif|png|jpg)$', 'http://imgs.xkcd.com/comics/python.png')
for match in p :
        print "Protokol: ", match.group(1) #http
        print "Poddomen: ", match.group(2) #imgs
        print "Domen: ", match.group(3) #xkcd
        print "Domennaya zona: ", match.group(4) #com
        print "Put na saite: ", match.group(5) #comics
        print "Name of file: ", match.group(6) #python
        print "Rasshirenie fayla: ", match.group(7) #png

>>> import re
>>> s = 'http://python.su/forum/viewtopic.php?id=8773'
>>> m = re.match('^(\w*)://(.*)/(.*)\?(.*)$',s)
>>> m.groups()
('http', 'python.su/forum', 'viewtopic.php', 'id=8773')
>>> m.groups()[1].split('/')
['python.su', 'forum']