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[Python-Dev] why _PyGen_Finalize(gen) propagates close() to _PyGen_yf() ?

Nathaniel Smith njs at pobox.com
Thu Mar 30 14:22:34 EDT 2017 
On Thu, Mar 30, 2017 at 11:05 AM, Oleg Nesterov <oleg at redhat.com> wrote:
> On 03/28, Eric Snow wrote:
>>
>> On Mon, Mar 20, 2017 at 11:30 AM, Oleg Nesterov <oleg at redhat.com> wrote:
>> > Hello,
>> >
>> > Let me first clarify, I do not claim this is a bug, I am trying to learn
>> > python and now I trying to understand yield-from.
>>
>> Given that you haven't gotten a response here,
>
> and this looks a bit strange. My question is simple, the implementation looks
> clear and straightforward, I am a bit surprised none of cpython devs bothered
> to reply.
>
>> you may want to take
>> this over to the core-mentorship at python.org list.
>
> Well, I'm afraid to contact this closed and not-for-mortals list, not sure
> this very basic question should go there ;) perhaps you are already a member,
> feel free to forward.

core-mentorship is intended as a friendly place for folks who are
starting to study CPython internals. I'm not sure where you got the
impression that it's not-for-mortals but I suspect the people running
it would like to know so they can fix it :-).

In any case the short answer to your original question is that PEP 342
says that generator finalization calls the generator's close() method,
which throws a GeneratorExit into the generator, and PEP 380 says that
as a special case, when a GeneratorExit is thrown into a yield from,
then this is propagated by calling .close() on the yielded-from
iterator (if such a method exists) and then re-raised in the original
generator.

-n

-- 
Nathaniel J. Smith -- https://vorpus.org
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