用户登录验证小程序~

db ={}
def newuser():
    prompt = 'login desired:'
    while True:
        name = raw_input(prompt)
        if db.has_key(name):
            prompt = 'name taken,try another.'
            continue
        else:
            break
    pwd = raw_input('passwd:')
    db[name] = pwd
def olduser():
    name = raw_input('login')
    pwd = raw_input('passwd')
    passwd = db.get(name)
    i = 0
    while i <3:
        if passwd == pwd:
            print 'welcome back',name
            break
        else:
            print 'passwd wrong ,try again.'
            i = i + 1
def showmenu():
    prompt = '''
    (N)ew User
    (E)xiting User Login
    (Q)quit
    enter choice
    '''
    done = False
    while not done :
        chose = False
        while not chose:
            try:
                choice = raw_input(prompt).strip()[0].lower()
            except (EOFError,KeyboardInterrupt):
                choice = 'q'
            print '\nYou picked"[%s]' % choice
            if choice not in 'neq':
                print 'invalid option, try again.'
            elif choice == 'n':
                newuser()
                chosen = True
                done = True
            elif choice == 'e':
                olduser()
                chosen = True
                done = True
            else :
                break
if __name__ == '__main__':
    showmenu()