Sorry for not describing this one particularly well.

There is nothing wrong with setattr() here, that wasn't the point.
Given the code below (py3, lambdas used for brevity):

    # coding: utf-8
    from cmd import Cmd

    class MyCmd(Cmd):
        def do_documented_at_definition(self):
            """ This one is documented with docstring. """
            pass
    
        def do_documented_afterwards(self):
            _ = 'This one will be documented afterwards, with help_<...>() method.'
        
    cli = MyCmd()
    cli.do_new_command = lambda *_: print("I'm new here")
    cli.help_documented_afterwards = lambda *_: print("I'm documenting")
    cli.cmdloop()


1. When one types in "help":
    1.1 there is no mention of "new_command" in the output, even though the command works.
    1.2 "documented_afterwards" command is being presented as having no documentation at all, but after typing "help documented_afterwards", it turns out that it is not the case.
2. There is no completion for "new_command", i.e. typing in "new_" and pressing tab key will not make it complete to "new_command".

I don't remember what was the use-case for this at the time (probably had something to do with disabling / enabling certain commands at runtime), but the implementation seemed trivial enough that we couldn't see justification for not doing it this way, hence the report.