Emitting events

After registering the events handlers, we can now emit corresponding events, which will cause all the registered handlers to be called in the order they were registered and will happen so within the EventController’s event loop.

Events can be emitted by calling the asyncio_event_hub.controller.EventController.emit method, that accepts the event (string, enum or integer) and positional and keyword arguments that get passed to all the event listeners (handlers).

Listing 6 Emitting event without waiting for it’s processing to complete

import asyncio
import asyncio_event_hub as aeh


def event_listener(a: int = 1):
    print(f"Called listener, a={a}")


async def main():
    ctrl = aeh.EventController()
    # Add a listener to "my_event", which always gets called
    # regardless of value a receives (no condition).
    ctrl.add_listener("my_event", event_listener)
    ctrl.start()  # Start the controller here.

    while True:
        await asyncio.sleep(5)
        ctrl.emit("my_event", a=10)  # Emit the event


asyncio.run(main())  # Start asyncio framework

Optionally we can also await for the events to be fully processed.

Listing 7 Emitting event and waiting for it’s processing to complete (await)

import asyncio
import asyncio_event_hub as aeh


def event_listener(a: int = 1):
    print(f"Called listener, a={a}")


async def main():
    ctrl = aeh.EventController()
    # Add a listener to "my_event", which always gets called
    # regardless of value a receives (no condition).
    ctrl.add_listener("my_event", event_listener)
    ctrl.start()  # Start the controller here.

    while True:
        await asyncio.sleep(5)
        await ctrl.emit("my_event", a=10)  # Emit the event


asyncio.run(main())  # Start asyncio framework

Event priority

Asyncio Event Hub allows to prioritize events. Events with higher priority always get emitted before the ones with lower priority. The asyncio_event_hub.controller.EventController.emit method accepts a keyword argument priority to control the priority level. It is an integer parameter, where a higher integer means higher priority. The default priority is 0.

Listing 8 Emitting event and waiting for it’s processing to complete (await)

import asyncio
import asyncio_event_hub as aeh


def event_listener(a: int = 1):
    print(f"Called listener, a={a}")


async def main():
    ctrl = aeh.EventController()
    # Add a listener to "my_event", which always gets called
    # regardless of value a receives (no condition).
    ctrl.add_listener("my_event", event_listener)
    ctrl.start()  # Start the controller here.

    while True:
        await asyncio.sleep(5)
        # Emit the event with a=10
        ctrl.emit("my_event", a=10)
        # Emit the event with a=20. This will be executed before a=10 one.
        ctrl.emit("my_event", a=20, priority=1)

asyncio.run(main())  # Start asyncio framework