On Wed, Jan 29, 2014 at 8:30 PM, Paul Tagliamonte <[email protected]> wrote:
> I love asyncio so far, nice work, huge step forward!
>
Thanks!
> Running the following minimal example:
>
> /
> | import asyncio
> | from asyncio.base_events import BaseEventLoop
>
> You most likely shouldn't be doing this. That class is not a complete
implementation, just a base with some parts of the implementation that is
widely shared. The rest of the implementation is in various subclasses
whose name isn't published -- and *which* class is used is determined
dynamically at run time (either by the app or by the event loop policy).
> |
> | class TestEventLoop(BaseEventLoop):
> | def something_important(self, arg):
> | # Do something important with arg.
> | pass
> |
> |
> | def print_and_repeat(loop):
> | print('Hello World')
> | loop.call_later(2, print_and_repeat, loop)
> |
> |
> | asyncio.set_event_loop(TestEventLoop())
> |
> |
> | loop = asyncio.get_event_loop()
> | loop.call_soon(print_and_repeat, loop)
> | loop.run_forever()
> \
>
> Results in the following traceback:
>
> /
> | Traceback (most recent call last):
> | File "test.py", line 21, in <module>
> | loop.run_forever()
> | File "/usr/lib/python3.4/asyncio/base_events.py", line 153, in
> run_forever
> | self._run_once()
> | File "/usr/lib/python3.4/asyncio/base_events.py", line 614, in
> _run_once
> | event_list = self._selector.select(timeout)
> | AttributeError: 'TestEventLoop' object has no attribute '_selector'
> \
>
> it appears there's some magic before actually setting the event loop.
>
There's nothing wrong with your set_event_loop() call, just with your event
loop class...
> What's the proper way to set the event loop? I really don't want to
> re-implement the entire EventLoop class, I just want to add a few
> methods for a quirky usecase I have.
>
Does what you want to add *have* to be an event loop method? If you make
it a function that takes a loop argument you don't have to deal with the
subclassing.
If you really can't do it any other way, and you really need to inherit
from the event loop, you can inherit from asyncio.SelectorEventLoop, which
is an alias for the real selector-based event loop (the concrete class
varies by platform). But then you won't be supporting IOCP on Windows. And
you probably shouldn't get too comfortable doing that.
--
--Guido van Rossum (python.org/~guido)
