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

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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