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The problem I was having specifically was that the url had a
colon in the query string. Since the query string was being
parsed as part of the host, the text after the colon was
being treated as the port when urllib.splitport was called
later. The following is a simple testcase:

import urllib2
webpage = urllib2.urlopen("http://host.com?a=b:3b")

You will then get a "httplib.InvalidURL: nonnumeric port: '3b'"