使用Python 3 实现简易用户登录系统，输错三次密码锁定账号。
文件结构：
lock.txt
保存被锁定的用户，一行一个
users.txt
保存用户账号密码，按照以下格式
{"jack":"1234","tom":"123","alex":"12345"}
login.py
import getpass # 使用getpass模块，输入密码的时候是密文
import json
username = input("input username:")
with open("users.txt",'r') as f: # 用户表，保存用户名和密码
contents = f.read()
users = json.loads(contents) # convert to dict type
with open("lock.txt",'r') as lock_file: # lock.txt保存被锁定用户，这里读取出来用于判断用户输入的账号是否已经被锁定
lock_users = lock_file.readlines()
lock_user_list=list()
for lock_user in lock_users:
lock_user_list.append(lock_user.strip()) # 转换成列表，并去除每个元素后面的换行符
if username in lock_user_list:
print("your account {username} has been locked, please contact the administrator.".format(username=username)) # 字符串格式化，在lock.txt直接退出
exit()
count = 0 # 计数器，用于统计用户输入密码次数
count_left = 3 # 还剩几次
if username in users: # 外层循环，判断用户是否存在，不存在直接退出，存在则进入密码输入环节
while count < 3: # 计数3次
#password = input("input your password:")
password = getpass.getpass("input your password:") # getpass模块
if password == users[username]:
print("welcome aboard, {username}!".format(username = username))
break
else:
count_left -= 1
while count_left:
print("invalid password, try again and {count_left} times left!".format(count_left=count_left))
break
count += 1
else:
print("invalid password, try maximum times, your account has been locked.") # 尝试超过最大次数限制，锁定账户，将username存进lock.txt，一行一个
block = open("lock.txt","a")
block.write(username+'\r')
block.close()
else:
print("no such username: {username}, exit.".format(username=username))
exit()