如果登录时，输入密码错误，将锁定此人。
需要通过文件 user.txt 放入每个用户名和密码
需要通过文件 lock.txt 放入锁定用户的用户名

#set encoding=utf-8
user = open('user_np.txt')
account_list = user.readlines()
user.close()
lock_n = False #判断用户输入的用户名是否被锁的标志位
while True:
    username = input('please input username:').strip() #strip()函数是忽略空格
    if len(username) == 0:
        print('输入用户名不能为空')
        continue
    else:
        l = open('lock.txt')
        l_list = l.readlines()
        l.close()
        for j in l_list:
            j = j.strip('\n')
            if username == j:
                print('该用户已经锁定，请联系管理员')
                lock_n = True
                break
        else:
            for i in account_list:
                i = i.split()       #split()函数是对括号中的符号进行切割
                if username == i[0]:
                    for x in range(3):
                        password = input('please input password:').strip()
                        if password == i[1]:
                            print('您可以进入系统')
                            exit(0)
                        else:
                            print('The password is error.')
                    print('%s ,input password is beyond three times,going to lock'%username)
                    l = open('lock.txt','a')
                    l.write(username+'\n')      #将要锁的用户名写入锁文件并且换行
                    l.close()
            print('没有这个用户')