#元组也是List,但是值不能变

a=('','','')

print(a[1])

mysql=('127.0.0.1','',''root','123456')

print(mysql.count('root'))

#例子

all_user={}

while True:

    username=input('username:').strip()

    passwd=input('passwd:').strip()

    cpwd=input('cpwd:').strip()

    if username and pwd and cpwd:

        if username in all_user:

            print('用户名已经存在')

        else:

            if pwd==cpwd :

                all_user[username]=passwd

            else:

                print('两次密码不一致')

    else:

        print('账号密码不能空')

#登录例子

all_users={}

while True:

    username=input('username:').strip()

    passwd=input('passwd:').strip()

    if username and passwd:

       if username in all_users:

           passwd=all_users[username]

           if passwd==all_users[username]:

              print('登录成功')

              break

           else:

              print('密码错误')

       else:

          print('用户名不存在')

    else:

        print('用户密码不能为空')