Python 3 chat server example using select.select()

tcp-chat-server.py

#!python3

"""
To use this program, open three or more terminal/console windows
    python3 tcp-chat-server.py

in all remaining windows:
    nc localhost 5678

OR 
    telnet localhost 5678

To enable telnet on Windows 10
  https://social.technet.microsoft.com/wiki/contents/articles/38433.windows-10-enabling-telnet-client.aspx

Based on the example:
  https://steelkiwi.com/blog/working-tcp-sockets/

See also:
  https://docs.python.org/3.6/library/select.html?highlight=select.select#select.select
  https://docs.python.org/3/howto/sockets.html
"""

import select
import socket
import sys
import queue

ip_address = 'localhost'
port = 5678
listen_queue_depth = 5

welcome = b'Welcome. Type text to echo a message or *text to broadcast to all connected clients.\n'


def main():
    server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    server.setblocking(0)

    server.bind((ip_address, port))
    server.listen(listen_queue_depth)
    print(f'[Server] server={server} fileno={server.fileno()}')
    print(f'[Listening] ip_address={ip_address} port={port}')

    inputs = [server]
    outputs = []
    message_queues = {}

    while inputs:
        readable, writable, exceptional = select.select(
            inputs, outputs, inputs)

        for s in readable:

            if s is server:
                # new connection (on the server socket)

                connection, client_address = s.accept()
                connection.setblocking(0)
    
                inputs.append(connection)
                message_queues[connection] = queue.Queue()

                message_queues[connection].put(welcome)
                outputs.append(connection)

                print(f'[New connection] socket={s} fileno={s.fileno()}')

            else:
                # data from an existing connection (on the socket for this connection)
                byte_data = s.recv(1024)

                if byte_data:
                    # Do something with out new data 
                    # i.e. broadcast to all connected clients or echo to one client

                    data = str(byte_data, 'utf-8')

                    if str(data)[0] == '*':
                        print(f'[Broadcast Data] fileno={s.fileno()} data={data}')

                        for bs in message_queues:
                            message_queues[bs].put(b'broadcast=' + bytes(data[1:], 'utf-8'))

                            if bs not in outputs:
                                outputs.append(bs)

                    else:
                        print(f'[Echo Data] fileno={s.fileno()} data={data}')
                        message_queues[s].put(b'echo=' + bytes(data, 'utf-8'))

                        if s not in outputs:
                            outputs.append(s)

                else:
                    if s in outputs:
                        outputs.remove(s)

                    inputs.remove(s)
                    s.close()
                    del message_queues[s]

        for s in writable:
            try:
                next_msg = message_queues[s].get_nowait()

            except queue.Empty:
                outputs.remove(s)

            else:
                print(f'[Send next message] fileno={s.fileno()} data={next_msg}')
                s.send(next_msg)

        for s in exceptional:
            print(f'[Exception] fileno={s.fileno()}')

            inputs.remove(s)

            if s in outputs:
                outputs.remove(s)

            s.close()
            del message_queues[s]


if __name__ == '__main__':
    main()