Build a Simple UDP Chatroom with Python Sockets – Step‑by‑Step Guide

1. Introduction

Sockets are endpoints of a two‑way communication channel. They can be used for inter‑process communication on the same machine or across different hosts that have Internet connectivity.

2. Socket module

To create a socket you call socket.socket() with the family, type and optional protocol arguments:

s = socket.socket(socket_family, socket_type, protocol=0)

3. Common methods

Typical socket methods used in the examples include bind(), sendto(), recvfrom(), and close().

4. Example 1 – Simple UDP chat

4.1 Server

# server.py
import socket

s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
host = socket.gethostname()
port = 8088
s.bind((host, port))
try:
    while True:
        receive_data, addr = s.recvfrom(1024)
        print("From server " + str(addr) + " message:")
        print(receive_data.decode('utf-8'))
        msg = input('please input send to msg:')
        s.sendto(msg.encode('utf-8'), addr)
except:
    s.close()

4.2 Client

# client.py
import socket

s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
while True:
    host = socket.gethostname()
    port = 8088
    send_data = input('please input msg:')
    s.sendto(send_data.encode('utf-8'), (host, port))
    msg, addr = s.recvfrom(1024)
    print("From server " + str(addr) + " message:")
    print(msg.decode('utf-8'))

5. Optimized multi‑user chatroom

5.1 Server

# server.py
import socket, logging

def main():
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    addr = ('127.0.0.1', 9999)
    s.bind(addr)
    logging.info('UDP Server on %s:%s...', addr[0], addr[1])
    users = {}
    while True:
        try:
            data, addr = s.recvfrom(1024)
            if addr not in users:
                for address in users:
                    s.sendto(data + b' 进入聊天室...', address)
                users[addr] = data.decode('utf-8')
                continue
            if 'exit' in data.decode('utf-8').lower():
                name = users.pop(addr)
                for address in users:
                    s.sendto((name + ' 离开了聊天室...').encode(), address)
                continue
            print('"%s" from %s:%s' % (data.decode('utf-8'), addr[0], addr[1]))
            for address in users:
                if address != addr:
                    s.sendto(data, address)
        except ConnectionResetError:
            logging.warning('Someone left unexpectedly.')
if __name__ == '__main__':
    main()

5.2 Client

# client.py
import socket, threading

def recv(sock, server):
    """Receive messages; a UDP socket must send once before receiving on Windows."""
    sock.sendto(name.encode('utf-8'), server)
    while True:
        data = sock.recv(1024)
        print(data.decode('utf-8'))

def send(sock, server):
    """Send messages."""
    while True:
        string = input()
        message = name + ' : ' + string
        data = message.encode('utf-8')
        sock.sendto(data, server)
        if string.lower() == 'exit':
            break

def main():
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    server = ('127.0.0.1', 9999)
    tr = threading.Thread(target=recv, args=(s, server), daemon=True)
    ts = threading.Thread(target=send, args=(s, server))
    tr.start()
    ts.start()
    ts.join()
    s.close()

if __name__ == '__main__':
    print("-----欢迎来到聊天室,退出聊天室请输入'EXIT(不分大小写)'-----")
    name = input('请输入你的名称:')
    print('-----------------%s------------------' % name)
    main()

This simple UDP chatroom supports multiple users communicating through a single server.