Python入门——简单明了的实现：用户注册及登录

#coding:utf-8
'''
    这个程序管理用于登录系统的用户信息：登录名字和密码。登录用户帐号建立后，已存在用户
    可以用登录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帐号。
'''
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
    Example 7.1 Dictionary Example (userpw.py) (continued)
    Enter choice: """

    done = False
    while not done:
        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
                done = True
                newuser()
                olduser()

if __name__ == '__main__':
    showmenu()

代码来源——《Python核心编程》