Python实战：登录系统

import string,datetime

FILE_NAME = "user.txt" #常量

def get_all_user():
    users = {}
    with open(FILE_NAME,'a+',encoding="utf-8") as fr:
        fr.seek(0)
        for line in fr: #xiaohei,123456
            if line.strip(): #是否为空行
                username, password = line.strip().split(',')
                users[username] = password
    return users

def check_password(password):
    return set(password) & set(string.ascii_uppercase) and set(password) &  \
    set(string.ascii_lowercase) and set(password) & set(string.digits) \
    and len(password)>=8 and len(password)<=12

def check_username(username):
    return len(username)>=6 and len(username)<=12


for i in range(3):
    username = input("username:").strip()
    password = input("password:").strip()
    if not check_username(username):
        print("用户名必须长度必须6-12")
        continue
    if not check_password(password):
        print("密码必须长度必须8-12，必须包含大小写字母、数字")
        continue
    all_user = get_all_user()
    if username in all_user:
        f_password = all_user.get(username)
        if f_password == password:
            print("登录成功！今天的日期是 %s" %datetime.datetime.today() )
            break
        else:
            print("密码错误！")
    else:
        print("用户不存在")

else:
    print("错误次数过多，最多可以输入3次")