The docstring says "This may be None or an instance of EventLoop". But docs explicitly state that get_event_loop "must never return None". The same docstring is also in the example in docs: https://docs.python.org/3.6/library/asyncio-eventloops.html#customizing-the-event-loop-policy

I propose changing it to:

def get_event_loop(self):
    """Get the event loop.

    Returns an instance of EventLoop or raises an exception.
    """

If the wording is ok, I'll make a PR.