[Python-Dev] PEP 479: Change StopIteration handling inside generators

[Guido van Rossum]

On Mon, Nov 24, 2014 at 4:21 PM, Alexander Belopolsky <
alexander.belopolsky at gmail.com> wrote:

>
> On Wed, Nov 19, 2014 at 3:10 PM, Guido van Rossum <guido at python.org>
> wrote:
>
>> There's a new PEP proposing to change how to treat StopIteration bubbling
>> up out of a generator frame (not caused by a return from the frame). The
>> proposal is to replace such a StopIteration with a RuntimeError (chained to
>> the original StopIteration), so that only *returning* from a generator (or
>> falling off the end) causes the iteration to terminate.
>
>
> I think the PEP should also specify what will happen if the generator's
> __next__() method is called again after RuntimeError is handled.  The two
> choices are:
>
> 1. Raise StopIteration (current behavior for all exceptions).
> 2. Raise RuntimeError (may be impossible without gi_frame).
>
> I think choice 1 is implied by the PEP.
>

Good catch. It has to be #1 because the generator object doesn't retain
exception state. I am behind with updating the PEP but I promise I won't
mark it as Accepted without adding this, the transition plan, and a
discussion of some of the objections that were raised.

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