shell.py

from cmd import Cmd

class MyPrompt(Cmd):

    def do_hello(self, args):
        """Says hello."""
        print "Hello, world"

    def do_quit(self, args):
        """Quits the program."""
        print "Quitting."
        raise SystemExit


if __name__ == '__main__':
    prompt = MyPrompt()
    prompt.prompt = '> '
    prompt.cmdloop('Starting prompt...')