aio pubsub pattern

pubsub.py

from collections import defaultdict
from asyncio import gather


class Pubsub:
    channels = defaultdict(list)

    def add_handler(self, key: str, handler):
        self.channels[key].append(handler)

    async def handle(self, ctx, key: str, event):
        await gather(*(handler(ctx, event) for handler in self.channels[key]))