flag跳出多层循环

# 有时候我们需要从第三层的for循环直接跳出第二层的while循环,进入第一层循环,只用break就做不到了,这时候我们可以用flag.

# (1)用法1: 定义标识为Ture,然后while flag,比如验证登录信息,验证成功直接改变标识状态为False,直接跳到第一层while循环(不执行else里的代码)/如果验证完都没成功,那么久执行else里面的代码
    n = 1
    while 1:
        # 阻塞等待客户端连接
        conn, addr = server.accept()
        print('第%d个客户端连接成功' % n)
    
        flag = True
        count = 1
        while flag:
            try:
                # 阻塞,等待接收
                data = conn.recv(1024)
                data = data.decode('utf-8')
                a, b = data.split('_')
                print(a, b)
    
                # 打开文件进行验证
                with open(r'D:\pythonproject\day28\02上次作业\2.用户登录作业\user_info', 'r') as f:
                    for line in f:
                        c, d = line.strip().split("_")
                        print(c, d)
                        if a == c and b == d:
                            conn.send('success'.encode('utf-8'))
                            flag = False
                            break
                    else:
                        if count < 3:
                            conn.send('fail'.encode('utf-8'))
                        elif count == 3:
                            conn.send('fail'.encode('utf-8'))
                            break
                        count += 1
            except ConnectionResetError:
                break

# (2)用法2: 在第二层while循环中,在执行某个操作之前定义标识(flag)状态,比如验证成功,就改变标识状态为Ture/验证完都不成过程,那么标识状态不变,之后根据标识状态再做操作.
    while 1:
        conn,addr=sock.accept()
        while 1:
            try:
                data=conn.recv(1024).decode("utf8")
                print("接收信息：",data)
                print("接收信息：",type(data))
                print("-----",data.split("|"))
                user,pwd=data.strip().split("|")
    
                # 文件操作
                flag=False
                with open("account","r") as f:
    
                    for line in f:
                        print("===",line.strip().split(":"))
                        username,password=line.strip().split(":")
                        if username==user and password==pwd:
                            flag=True
                            break
                if flag:
                    conn.send(b"success")
                    break
                else:
                    conn.send(b"fail")
            except Exception as e:
                print(e)
                break