'Display help about this program or one of its subcommands.'

@utils.arg('command', metavar='<subcommand>', nargs='?', help=_('Display    help    for    <subcommand>.'))
def do_help(self, args):

    if args.command:
        if (args.command in self.subcommands):
            self.subcommands[args.command].print_help()
        else:
            raise exc.CommandError((_("'%s'    is    not    a    valid    subcommand") % args.command))
    else:
        self.parser.print_help()
