54-字典练习：模拟注册/登陆

import getpass

userdb = {}

def register():
    username = input('username: ')
    if username in userdb:
        print('%s already exists.' % username)
    else:
        password = input('password: ')
        userdb[username] = password

def login():
    username = input('username: ')
    password = getpass.getpass("password: ")
    if userdb.get(username) != password:
        print('login failed')
    else:
        print('login successful')


def show_menu():
    cmds = {'0': register, '1': login}
    prompt = """(0) register
(1) login
(2) exit
Please input your choice(0/1/2): """

    while True:
        choice = input(prompt).strip()[0]
        if choice not in '012':
            print('Invalid inupt. Try again.')
            continue
        if choice == '2':
            break

        cmds[choice]()

if __name__ == '__main__':
    show_menu()