.. versionadded:: 0.1.0

Callbacks can also be :term:`coroutine functions <coroutine function>` (defined using :keyword:`async def` or decorated with :func:`@asyncio.coroutine <asyncio.coroutine>`). For this to work properly, the :class:`event loop <~asyncio.BaseEventLoop>` they belong to must be specified. This requirement is in place to prevent issues when multiple event loops are in use (via threads, etc).

The loop can be specified using the :any:`Dispatcher.bind_async` method, or passed as a keyword argument to :any:`Dispatcher.bind`.

import asyncio
from pydispatch import Dispatcher

class MyEmitter(Dispatcher):
    events = ['on_state']

class MyAsyncListener(object):
    def __init__(self):
        self.event_received = asyncio.Event()
    async def on_emitter_state(self, *args, **kwargs):
        self.event_received.set()

loop = asyncio.get_event_loop()
emitter = MyEmitter()
listener = MyAsyncListener()

# Pass the event loop as first argument to "bind_async"
emitter.bind_async(loop, on_state=listener.on_emitter_state)

async def trigger_and_wait_for_event():
    await asyncio.sleep(1)

    emitter.emit('on_state')

    # listener.event_received should be set from "on_emitter_state"
    await listener.event_received.wait()

loop.run_until_complete(trigger_and_wait_for_event())

import asyncio
from pydispatch import Dispatcher

class MyEmitter(Dispatcher):
    events = ['on_state']

class MyAsyncListener(object):
    def __init__(self):
        self.event_received = asyncio.Event()
    async def on_emitter_state(self, *args, **kwargs):
        self.event_received.set()

loop = asyncio.get_event_loop()
emitter = MyEmitter()
listener = MyAsyncListener()

# Pass the event loop using __aio_loop__
emitter.bind(on_state=listener.on_emitter_state, __aio_loop__=loop)

async def trigger_and_wait_for_event():
    await asyncio.sleep(1)

    emitter.emit('on_state')

    # listener.event_received should be set from "on_emitter_state"
    await listener.event_received.wait()

loop.run_until_complete(trigger_and_wait_for_event())

Event (and :any:`Property`) objects are :term:`awaitable`. This allows event subscription without callbacks in an async environment. The :any:`Event` instance itself must first be obtained using the :any:`Dispatcher.get_dispatcher_event` method. Any positional and keyword arguments from the event are returned as a two-tuple:

async def wait_for_event(event_name):
    event = emitter.get_dispatcher_event(event_name)
    args, kwargs = await event
    return args, kwargs

loop.run_until_complete(wait_for_event('on_state'))

This can also be done with :any:`Property` objects:

import asyncio
from pydispatch import Dispatcher, Property


class MyEmitter(Dispatcher):
    value = Property()
    async def change_values(self):
        for i in range(10):
            await asyncio.sleep(.1)
            self.value = i

class MyAsyncListener(object):
    async def wait_for_value(self, emitter):
        event = emitter.get_dispatcher_event('value')
        while True:
            args, kwargs = await event
            instance, value = args
            print(value)
            if value >= 9:
                break

loop = asyncio.get_event_loop()
emitter = MyEmitter()
listener = MyAsyncListener()

# Make the emitter value iterate from 0-9
asyncio.ensure_future(emitter.change_values())

# Listens for changes, then exits after value reaches 9
loop.run_until_complete(listener.wait_for_value(emitter))