python字典模拟登陆

[code]db={}
def newuser():
    prompt='Login desired: '
    while True:
        name=input(prompt)
        if name in db:
            prompt='name taken,try again'
        else:
            break;
    pwd=input('passwd: ')
    db[name]=pwd

def olduser():
    name=input('Login: ')
    pwd=input('passwd: ')
    realpwd=db.get(name)
    if pwd==realpwd:
        print('welcome back ',name)
    else :
        print('login incorrect')

menu={'n':newuser,'e':olduser}
def showmenu():
    prompt="""
(N)ew User Login
(E)xisting User Login
(Q)uit
Enter choice: """
    done=False
    while not done:
        chosen=False
        while not chosen:
            try:
                choice=input(prompt).strip()[0].lower()
            except(EOFError,KeyboardInterrupt):
                choice='q'
            print('\nYour choice:[%s]' % choice)
            if choice not in 'neq':
                print('invalid option')
            else :chosen=True
        if choice=='q':
            break
        menu[choice]()
if __name__=='__main__':
    showmenu()