[Python-ideas] PEP 3156 / Tulip: stopping the loop while in run_until_complete

[Saúl Ibarra Corretgé]

>
> I think there are actually two cases: where stop() is called from the
> task given to run_until_complete(), or from another task. In the former
> case, because the exception bubbles out of the task's coroutine, the
> task will be marked as done (and its exception set to _StopError) -- at
> least I think so. In the latter case, the task will still be runnable,
> and it will continue to run when the event loop is started again. (Hm...
> maybe run_forever() should be called start(), to match stop()?)
>
> I think your unittest only tests the former case.
>

Well, I think they are actually the same. In the gist I posted earlier I 
called loop.stop(), I didn't raise the exception inside the task, and 
loop.stop() will call call_soon so the actual raising will happen in the 
context on _run_once unless I'm mistaken.

Here is an updated simple test with it's output: 
https://gist.github.com/saghul/4758151

> I'm not sure what run_until_complete() should return in the latter case.
> In fact it makes me doubt the behavior of run_until_complete() in
> general. Maybe it should return the Future (although that's kind of
> redundant)? Or an enum indicating what happened? (Cases would be result,
> exception, timeout, running -- and maybe cancelled?)
>

I think the current behavior is ok, it the user really wants to check if 
the future was actually completed she can check with done(), if she 
saved the future in a variable, that is.

My other preferred approach would be to raise an exception, since I 
consider this an exceptional case: I told the loop to run until this 
future is completed so I expect that to happen. Since it didn't, 
NotCompletedError (or something alike) sounds good to me.


-- 
Saúl Ibarra Corretgé
http://saghul.net/blog | http://about.me/saghul