A simple python echo server.

echoserver.py

import asyncore
import asynchat
import socket

class Lobby(object):
    def __init__(self):
        self.clients = set()

    def leave(self, client):
        self.clients.remove(client)

    def join(self, client):
        self.clients.add(client)

    def send_to_all(self, data):
        for client in self.clients:
            client.push(data)

class Client(asynchat.async_chat):
    def __init__(self, conn, lobby):
        asynchat.async_chat.__init__(self, sock=conn)
        self.in_buffer = ""
        self.set_terminator("n")

        self.lobby = lobby
        self.lobby.join(self)

    def collect_incoming_data(self, data):
        self.in_buffer += data

    def found_terminator(self):
        if self.in_buffer.rstrip() == "QUIT":
            self.lobby.leave(self)
            self.close_when_done()
        else:
            self.lobby.send_to_all(self.in_buffer + self.terminator)
            self.in_buffer = ""

class Server(asynchat.async_chat):
    def __init__(self):
        asynchat.async_chat.__init__(self)
        self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
        self.set_reuse_addr()
        self.bind(("127.0.0.1", 12345))
        self.listen(5)
        self.lobby = None

    def set_lobby(self, lobby):
        self.lobby = lobby

    def handle_accept(self):
        sock, addr = self.accept()
        client = Client(sock, self.lobby)

if __name__ == '__main__':
    lobby = Lobby()
    server = Server()
    server.set_lobby(lobby)
    asyncore.loop()