Pure string operations :):
>>> url = "http://stackoverflow.com/questions/9626535/get-domain-name-from-url"
>>> url.split("//")[-1].split("/")[0].split('?')[0]
'stackoverflow.com'
>>> url = "stackoverflow.com/questions/9626535/get-domain-name-from-url"
>>> url.split("//")[-1].split("/")[0].split('?')[0]
'stackoverflow.com'
>>> url = "http://foo.bar?haha/whatever"
>>> url.split("//")[-1].split("/")[0].split('?')[0]
'foo.bar'
That's all, folks.