* Where are the tests?  A functional test, perhaps in test_urllib2net.py, for IPv6 support in urllib2 would be especially welcome, I think.
* Why does .check_host() not begin with an underscore?
* "check_host" is a poor name.  How about "_is_localhost"?
* locals is a built-in function, hence usually considered good style not to use it as a name.
* Is is necessary to call make_host_tuple(searchlist) twice?
* The patch appears to fix several bugs at once (e.g. adding a try: / except: suite around a large part of an existing method to catch socket.error).