asyncio support

New in version 0.1.0.

Callbacks

Callbacks can also be coroutine functions (defined using async def or decorated with @asyncio.coroutine). For this to work properly, the event loop 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 Dispatcher.bind_async method, or passed as a keyword argument to Dispatcher.bind.

Examples

bind_async method

>>> import asyncio
>>> from pydispatch import Dispatcher

>>> class MyEmitter(Dispatcher):
...     _events_ = ['on_state']
...     async def trigger(self):
...         await asyncio.sleep(1)
...         self.emit('on_state')

>>> class MyAsyncListener(object):
...     def __init__(self):
...         self.event_received = asyncio.Event()
...     async def on_emitter_state(self, *args, **kwargs):
...         print('received on_state event')
...         self.event_received.set()
...     async def wait_for_event(self):
...         await self.event_received.wait()

>>> 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)

>>> loop.run_until_complete(emitter.trigger())
>>> loop.run_until_complete(listener.wait_for_event())
received on_state event

bind (with keyword argument)

>>> import asyncio
>>> from pydispatch import Dispatcher

>>> class MyEmitter(Dispatcher):
...     _events_ = ['on_state']
...     async def trigger(self):
...         await asyncio.sleep(1)
...         self.emit('on_state')

>>> class MyAsyncListener(object):
...     def __init__(self):
...         self.event_received = asyncio.Event()
...     async def on_emitter_state(self, *args, **kwargs):
...         print('received on_state event')
...         self.event_received.set()
...     async def wait_for_event(self):
...         await self.event_received.wait()

>>> 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)

>>> loop.run_until_complete(emitter.trigger())
>>> loop.run_until_complete(listener.wait_for_event())
received on_state event

Async (awaitable) Events

Event (and Property) objects are awaitable. This allows event subscription without callbacks in an async environment. The Event instance itself must first be obtained using the 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 Property objects

>>> import asyncio
>>> from pydispatch import Dispatcher, Property

>>> class MyEmitter(Dispatcher):
...     value = Property()
...     async def change_values(self):
...         for i in range(5):
...             await asyncio.sleep(.1)
...             self.value = i
...         return 'done'

>>> class MyAsyncListener(object):
...     async def wait_for_values(self, emitter):
...         # Get the Event object for the Property
...         event = emitter.get_dispatcher_event('value')
...         # await the event until the value reaches 4
...         while True:
...             args, kwargs = await event
...             instance, value = args
...             print(value)
...             if value >= 4:
...                 break
...         return 'done'

>>> loop = asyncio.get_event_loop()
>>> emitter = MyEmitter()
>>> listener = MyAsyncListener()
>>> coros = [emitter.change_values(), listener.wait_for_values(emitter)]
>>> loop.run_until_complete(asyncio.gather(*coros))
0
1
2
3
4
['done', 'done']