pynng / Python pattern guide

pubsub communication topology

PUB / SUB — Topics and Broadcast

PUB / SUB broadcasts messages, while subscribers choose the topics they receive.

pynng is an independently maintained Python binding for NNG. Its maintainers and release cycle are separate from the NNG core project.

This example is sourced from the project’s default branch. See the upstream example for its current history.

pubsub.py

"""
This pattern is used to allow a single broadcaster to publish messages to many subscribers,
which may choose to limit which messages they receive.
"""

import datetime
import pynng
import trio

address = "ipc:///tmp/pubsub.ipc"


def get_current_date():
    return str(datetime.datetime.now())


async def server(sock):
    while True:
        date = get_current_date()
        print(f"SERVER: PUBLISHING DATE  {date}")
        await sock.asend(date.encode())
        await trio.sleep(1)


async def client(name, max_msg=2):
    with pynng.Sub0() as sock:
        sock.subscribe("")
        sock.dial(address)

        while max_msg:
            msg = await sock.arecv_msg()
            print(f"CLIENT ({name}): RECEIVED  {msg.bytes.decode()}")
            max_msg -= 1


async def main():
    # publisher publishes the date forever, once per second, and clients print as they
    # receive the date
    with pynng.Pub0(listen=address) as pub:
        async with trio.open_nursery() as nursery:
            nursery.start_soon(server, pub)
            nursery.start_soon(client, "client0", 2)
            nursery.start_soon(client, "client1", 3)
            nursery.start_soon(client, "client2", 4)


if __name__ == "__main__":
    try:
        trio.run(main)
    except KeyboardInterrupt:
        # that's the way the program *should* end
        pass
Run it

python -m pip install pynng trio
python pubsub.py