Ensure handler patterns are str, not unicode Python < 2.6.5 doesn't accept unicode keys in f(**kwargs), and base_project_url will always be unicode, which will in turn make the patterns unicode, and ultimately result in unicode keys in kwargs to handler._execute(**kwargs) in tornado. This enforces that base_project_url be ascii in that situation. Note that the URLs these patterns check against are escaped, and thus guaranteed to be ASCII: 'héllo' is really 'h%C3%A9llo'. If you actually use u'héllo' in your regex, it will not match the URLs you think it should.