^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$
raise error, v # invalid expression
sre_constants.error: nothing to repeat
>>> import re
>>> url = 'http://www.mail.ru/index.html'
>>> parser = re.compile('^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$')
>>> parser.findall(url)
[('http://', 'www.mail', 'ru', '')]