Minimal event bus?

EventBus.py

import asyncio
from collections import namedtuple

Event = namedtuple('Event',['source','data'])

observers = {}

def register(source, callback):
    observers.setdefault(source,[]).append(callback)

def notify(event):
    print(event)
    if event.source in observers:
        for observer in observers[event.source]:
            asyncio.ensure_future(observer(event))