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

[Guido van Rossum]

On Mon, Feb 11, 2013 at 2:23 PM, Saúl Ibarra Corretgé <saghul at gmail.com>wrote:

>
>
>> 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.
>

Oh, you're right! Not my day for reading carefully. :-)


> 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.
>

Good. How about calling future.result(), and letting it raise
InvalidStateError ? (Except if the timeout handler was called.)

-- 
--Guido van Rossum (python.org/~guido)
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