def do_a(*args): pass
def do_b(*args): pass

MY_COMMANDS = {
    'a': do_a,
    'b': do_b
}

def parse_command(s):
    cmd, *params = s.split()
    if cmd not in MY_COMMANDS:
        raise GtfoError
    return cmd, params

while True:
    cmd = raw_input('>>> ')
    cmd, params = parse_command(cmd)
    MY_COMMANDS[cmd](*params)