AmbiguousCommand is raised too soon. Right now, hg raises AmbiguousCommand as soon as it finds two commands/aliases that start with the substring it's searching for, even though it may still find a full match later on. This is a bit hard to hit on purpose, because hg checks the list of commands in whatever order is returned by table.keys(), which will change when you add an alias to a command. You should be able to hit it by adding an alias "u" to the "identify" command - not that that makes a lot of sense...

#!/usr/bin/env python
#
# An example CGI script to use hgweb, edit as necessary

import cgitb, os, sys
cgitb.enable()

# sys.path.insert(0, "/path/to/python/lib") # if not a system-wide install
from mercurial import hgweb

h = hgweb.hgweb("/path/to/repo", "repository name")
h.run()