UDP TypeError：+ 的不支持的操作数类型：“NoneType”和“str”

Question

我完全是 python 和计算机网络的新手。在从事 Uni 项目时，我遇到了一个问题。我究竟做错了什么？任何帮助我都会非常感激。

这里是服务器端：

import socket

def Main():
    host = "127.0.0.1"
    port = 5000

    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.bind((host, port))

    print ("Server Started.")
    while True:
        data, addr = s.recvfrom(1024)
        print ("message from: ") + str(addr)
        print ("from connected user: ") + str(data.decode('utf-8'))
        data = str(data).upper()
        print ("sending: ") + str(data)
        s.sendto(data, addr)

    s.close()

if __name__ == '__main__':
    Main()

这是我的客户端：

import socket

def Main():
    host = "127.0.0.1"
    port = 5000

    server = ('127.0.0.1', 5000)

    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.bind((host, port))

    message = input('->')
    while message != 'q':
        s.sendto(message.encode('utf-8'), server)
        data, addr = s.recvfrom(1024)
        print ('Received from server: ') + str(data)
        message = input('->')
    s.close()

if __name__ == '__main__' : 
    Main()

Answer 1

有几个问题；主要是印刷。

您有几个 print('some text') + str(data) 实例；这是行不通的，因为当print() 输出到屏幕（STDOUT）时它返回None，所以你实际上在做的是试图连接None + str(data)

你需要的是print('some text' + str(data))。

此外，服务器端存在问题，您将从客户端接收到的数据回显到客户端 - 它需要重新编码为字节数组（它以字节数组的形式出现，被转换为utf-8字符串显示，回复前需要回bytearray）。

总之，服务器：

import socket


def Main():
    host = "127.0.0.1"
    port = 5000

    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.bind((host, port))

    print("Server Started.")
    while True:
        try:
            data, addr = s.recvfrom(1024)
            print("message from: " + str(addr))  # moved string concatenation inside print method
            print("from connected user: " + str(data.decode('utf-8')))  # moved string concatenation inside print method
            data = str(data).upper()
            print("sending: " + str(data))  # moved string concatenation inside print method
            s.sendto(data.encode('utf-8'), addr)  # needed to re-encode data into bytearray before sending
        except KeyboardInterrupt:  # added for clean CTRL + C exiting
            print('Quitting')
            break

    s.close()


if __name__ == '__main__':
    Main()

还有客户：

import socket


def Main():
    host = "127.0.0.1"
    port = 5001

    server = ('127.0.0.1', 5000)

    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.bind((host, port))

    message = input('->')
    while message != 'q':
        try:
            s.sendto(message.encode('utf-8'), server)
            data, addr = s.recvfrom(1024)
            print('Received from server: ' + str(data))  # moved string concatenation inside print method
            message = input('->')
        except KeyboardInterrupt:  # added for clean CTRL + C exiting
            print('Quitting')
            break

    s.close()


if __name__ == '__main__':
    Main()