一旦有了多个函数，则通常需要一个函数能够把他们全部聚集在一起，这个函数通常叫做main() ``` def main(): username = get_username() password= get_password() authenticated = authenticate(user=username,password=password) if authenticated: print_timesheet(username) add_hours(username) def get_username(): return sanqian def get_password(): return 123456 if __name__ == "__main__": main() ```