Python 模拟登陆数据系统

#!/usr/bin/python
#--*-- coding:utf-8 --*--
"""
此程序管理用于登陆系统的用户信息：登陆名字和密码。登陆用户账号建立后，已存在用户可以用
登陆名字和密码重返系统。新用户不能用别人的登录名建立用户账号
"""
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)
    if passwd == pwd:
        print 'welcome back',name
    else:
        print 'login incorrect!'

def showmenu():
    prompt = """
    (N)ew User Login
    (E)xisting User Login
    (Q)uit
    Enter choice: """

    done = False
    chosen = False
    while not chosen:
        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'
        else:
            chosen = True
    if choice == 'q':done = True
    if choice == 'n':newuser()
    if choice == 'e':olduser()

if __name__ == '__main__':
    while True:
        showmenu()