async def make_stream():
    loop = asyncio.get_event_loop()
    queue = asyncio.Queue()
    def callback(message):
        loop.call_soon_threadsafe(queue.put_nowait, message)
    async def stream():
        while True:
            yield queue.get()
    return callback, stream()

async def print_messages():
    # print messages as they come
    cb, stream = make_iter()
    mido.open_input(callback=cb)

    async for message in stream:
        print(message)