import asyncio

from graia.broadcast import Dispatchable, BaseDispatcher, Broadcast
from graia.broadcast.interfaces.dispatcher import DispatcherInterface

class ExampleEvent(Dispatchable):
    class Dispatcher(BaseDispatcher):
        def catch(interface: "DispatcherInterface"):
            if interface.annotation is str:
                return "ok, i'm."

loop = asyncio.get_event_loop()
broadcast = Broadcast(loop)

@broadcast.receiver("ExampleEvent") # or just receiver(ExampleEvent)
async def event_listener(maybe_you_are_str: str):
    print(maybe_you_are_str) # <<< ok, i'm

async def main():
    broadcast.postEvent(ExampleEvent()) # sync call is allowed.
    await asyncio.sleep(0.1) # to solve event task.

loop.run_until_complete(main())