Well, three occurrences means you only have three methods to patch (and two of them are trivial).  But I agree that copying the non-trivial method doesn't look fun from a maintenance perspective.

You could also try using an object that is not a subclass of str.  The problem with subclassing str is that some (most?) string methods do not do a subclass check but directly call the C implementation of the method.  I think there's an issue in the tracker somewhere about that.

The problem with not subclassing string, of course, is that you may end up implementing a lot of methods on your object to get it to play nicely with urllib2's assumption that it *is* a string.