Allow coroutine functions in callbacks

[acrisci]

The high-level client on_[SIGNAL]() and low-level add_message_handler() should accept coroutine functions as handlers in addition to normal functions.

[e-sr]

Hi, i would expect a signal to be be an awaitable? Why use a callback?

[acrisci]

This is just how I do events I guess.

What would awaitable events look like? Do you have an example from another library?

[e-sr]

awaitable.

For example if looking at zmq sockets when you subscrie with a with a SUB socket to a PUB socket you await a publication

msg= await sub_socket.recv()

I expected something similar on dbus signals

signal = await bus.signal()

[michallowasrzechonek-silvair]

It's easy to implement on the client side using asyncio.Queue. The callback does put_nowait and you can await on the get.