Thanks for explaining this more.

I am surprised that a 301 redirect would give an invalid port -- but surely webmasters aren't perfect. :-)

The argument that urllib.Urlopener.open() checks for socket.error but not for other errors is a good one.

However I don't see the httplib.py code raising socket.error elsewhere.  I'll ask Jeremy.  The rest of the module seems to be using a totally different set of exceptions.  On the other hand, it *can* raise socket.error, implicitly (when various socket calls are being made).