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...

def demandload(scope, modules):
    class d:
        def __getattr__(self, name):
            mod = self.__dict__["mod"]
            scope = self.__dict__["scope"]
            scope[mod] = __import__(mod, scope, scope, [])
            return getattr(scope[mod], name)

    for m in modules.split():
        dl = d()
        dl.mod = m
        dl.scope = scope
        scope[m] = dl