登录和注册，要自己建user表，注册进来的密码要加密加盐1

#select * from user where username="%s";' % username

#登陆

import hashlib
import string, datetime

import pymysql


# 检查用户是否在数据库中
def check_user_exist(username):
    sql = "select pw_md5 from %s where uname = '%s'" % (table_name, username)
    cur.execute(sql)
    db = cur.fetchall()
    if db:
        return db[0].get('pw_md5')  # 如果用户存在，返回该用户的加密密码
    else:
        return None


# 给密码加密加盐
def my_md5(s, salt=""):
    new_s = str(s) + salt
    m = hashlib.md5(new_s.encode())
    return m.hexdigest()


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


mysql_info = {
    "host": "118.24.3.140",
    "user": "jxz",
    "password": "123456",
    "port": 3306,
    "charset": "utf8",
    "autocommit": True,
    'db': 'jxz'
}

conn = pymysql.connect(**mysql_info)  # 连接数据库，必须加**，因为是多个参数
cur = conn.cursor(pymysql.cursors.DictCursor)
table_name = 'users'

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
    if check_user_exist(username):
        if my_md5(password) == check_user_exist(username):
            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")
    cur.close()
    conn.close()