My users submit urls (to mixes on mixcloud.com) and my app uses them to perform web requests.
A good url returns a 200 status code:
I can't figure out how to comment on the accepted answer (this question might be closed), but I should note that r.header is now obsolete, so r.header['location'] should be replaced by r['location'] (per https://stackoverflow.com/a/6934503/1084675 )
r.header
r.header['location']
r['location']