服务端代码：

import socket
import threading
import logging
import datetime
logging.basicConfig(format='%(thread)s %(threadName)s %(message)s',level=logging.INFO)

class ChatServerUdp:
    def __init__(self,ip='127.0.0.1',port=9988):
        self.sock = socket.socket(type=socket.SOCK_DGRAM)
        self.addr = (ip,port)
        self.event = threading.Event()
        self.clients = {}
        self.interval = 10

    def start(self):
        self.sock.bind(self.addr)
        threading.Thread(name='recv',target=self._recv,daemon=True).start()

    def stop(self):
        self.sock.close()
        self.event.set()

    def _recv(self):
        while not self.event.is_set():
            print(self.clients)
            data,clientaddr = self.sock.recvfrom(1024)
            logging.info('{} {}'.format(data.decode(),clientaddr))
            data = data.decode().strip()

            current = datetime.datetime.now().timestamp()


            if data == '^hb^':
                self.clients[clientaddr] = current
                continue

            elif data == 'quit':
                self.clients.pop(clientaddr)
                continue

            elif data == 'come':
                self.clients[clientaddr] = current
                continue

            self.clients[clientaddr] = current

            msg = 'ack {}'.format(data)
            n = datetime.datetime.now().timestamp()
            lst = set()

            for caddr,ts in self.clients.items():
                if n - ts <= self.interval:
                    print(self.clients)
                    self.sock.sendto(msg.encode(),caddr)
                else:
                    lst.add(caddr)

            for x in lst:
                self.clients.pop(x)

cs = ChatServerUdp()
cs.start()

while True:
    cmd = input('>>>').strip()
    if cmd == 'quit':
        cs.stop()
        break

客户端代码：

import threading
import socket
import logging
logging.basicConfig(format='%(thread)s %(threadName)s %(message)s',level=logging.INFO)

class ChatClientUdp:
    def __init__(self,ip='127.0.0.1',port=9988,interval=5):
        self.sock = socket.socket(type=socket.SOCK_DGRAM)
        self.addr = (ip,port)
        self.interval = interval
        self.event = threading.Event()

    def start(self):
        self.sock.sendto(b'come',self.addr)
        threading.Thread(name='revfrom',target=self._recv,daemon=True).start()
        threading.Thread(name='hb',target=self._sendhb,daemon=True).start()

    def _recv(self):
        while not self.event.is_set():
            data,srvaddr = self.sock.recvfrom(1024)
            logging.info('{} {}'.format(data.decode(),srvaddr))

    def send(self,data='quit'):
        self.sock.sendto(data.encode(),self.addr)

    def _sendhb(self):
        msg = '^hb^'
        while not self.event.wait(self.interval):
            self.sock.sendto(msg.encode(),self.addr)

    def stop(self):
        self.sock.close()

cc = ChatClientUdp()
cc.start()

while True:
    cmd = input('>>>').strip()
    if cmd == 'quit':
        cc.send('quit')
        cc.stop()
        break
    cc.send(cmd)

运行结果：
服务端：

{}
>>>{('127.0.0.1', 36163): 1563519226.766523}
140093223106304 recv ^hb^ ('127.0.0.1', 36163)
{('127.0.0.1', 36163): 1563519231.767525}
140093223106304 recv ^hb^ ('127.0.0.1', 36163)
140093223106304 recv ^hb^ ('127.0.0.1', 36163)
{('127.0.0.1', 36163): 1563519236.766653}
{('127.0.0.1', 36163): 1563519237.175765}
{('127.0.0.1', 36163): 1563519237.175765}
140093223106304 recv hello python ('127.0.0.1', 36163)
{('127.0.0.1', 36163): 1563519241.766967}
140093223106304 recv ^hb^ ('127.0.0.1', 36163)
{}
140093223106304 recv quit ('127.0.0.1', 36163)

客户端：

>>>hello python
>>>139819724605184 revfrom ack hello python ('127.0.0.1', 9988)
quit