Interprocess Communication in Python using multiprocessing.connection's Listener, Client

multiprocessing_ipc.py

"""
No Copyright by the way.
Usage:
0. Have two terminals
1. In the first terminal run `test.py`
2. In the second terminal run `test.py a`
3. Magic! If you don't see anything, the arbitrary port 12025 may be in use so use another port

Practical applications (requires more than just copy pasting this code):
    - Simple message queueing:
        - Start a Listener with multiprocess.Process and give it long tasks (e.g. sending an email, generating graphics)
    - Communicating with an already running instance of the app without needing a micro web framework

I use 127.0.0.1 instead of localhost because resolving the localhost is a performance hinderence.
You can use ::1 or whatever the IPv6 version is if you want to use IPv6.
"""
from multiprocessing.connection import Listener, Client
import sys

HOST = '127.0.0.1'
PORT = 12025

if len(sys.argv) == 1:
    print('Listener Mode')
    listener = Listener((HOST, PORT), authkey=b'abc')
    while True:
        # Each new Client() requires an acception from the listener
        # Lisnenr can only interact with one client at a time
        # since web app has multiple workers, easier to have multiple clients when needed
        with listener.accept() as conn:
            a = conn.recv()
            b = conn.send('from listener')
            if a == 'exit':
                print('exit got')
                sys.exit()
    # use client
else:
    print('Client Mode')
    with Client((HOST, PORT), authkey=b'abc') as c:
        c.send('test')
        print('sent!')
        print(c.recv())

    with Client((HOST, PORT), authkey=b'abc') as c:
        c.send('exit')
        print('sent v2!')
        print(c.recv())