1. The current code in cmd.get_names does a dir on the derived class for
   cmd.Cmd object instead, which means that if I do something similar to
   the following:

class CLI(cmd.Cmd):
   def register_subcommand(self, cmd, cli_class):
       def call_cli(self):
           cli = cli_class()
           cli.cmdloop()
       setattr(self, 'do_%s' % (cmd, ), call_cli)

   it won't register the command in the completion list or help list.

2. Registering a do_EOF handler is a bit of a hack to work around
   the fact that entering in ^D on the command line prints out:

   (Cmd) *** Unknown syntax: EOF

   I can't speak to the fact that my desired behavior should be 
   enforced (basically trickle up the EOFError like so):

   def do_EOF(self, arg):
       raise EOFError

   so what I'm proposing instead is that it be filtered out by default.

Given that there's some value in allowing developers to build custom filter rules for the completions (example: certain commands can be undocumented, hidden to lower privilege users, etc), I figured it would be wise to create a custom mechanism for filtering out commands.

This could be cleaned up to use better python idioms like a generator, cache the data and have a refresh method, etc, but this is a good first start.

This looks to be a reasonable request.

I think the patch would be better if the filtering were done directly in get_names().  A subclass can override or extend that method if it wants to customize the filter.

Here's a version incorporating your suggestion and better documenting the choices and the method for overriding purposes. I have a few reservations with the current implementation:

1. As noted, the information for the class really could be and should be cached as the attributes of a given cmd.Cmd derived class don't change all that frequently.
2. One has to override the entire function in order to get what I consider standard functionality (filtering).. so I don't know if that's a good idea.
3. I've thought about the do_EOF handler stuff, and it would be nice if that was shoved into the completer method(s) as a keyword argument, defaulting to False -- that way one could avoid having to explicitly install an EOF handler when dealing with ^D, etc, but this can be hashed out better in a different issue, over IRC, email, etc.

This module could be better cleaned up (isn't PEP8 compliant, overrides built-ins, is pythonic but not super pythonic, etc), but I'll see what other modules exist out there that could be used in its place, because they could have resolved some of these issues. There is some value that can be obtained from pexpect, some of the other cmd module variants, etc .. I just like this module because it's nice, simple, and standard -- it just needs a little love and it will be awesome.

Anyhow -- thanks again for the work :).

Needed to update the patch slightly for Python 3; now that filter() returns an iterator, ``do_help``'s call to 
names = self.get_names()
followed by
            names.sort()
was throwing an error, so I changed get_names to return a list.

Change to test_cmd.py to test for help displaying the name of the registered subcommand (as well as a simple test for the basic operation of the registered sub-CLI).