[Python-Dev] PEP 550 v4

Koos Zevenhoven k7hoven at gmail.com
Wed Sep 6 11:07:36 EDT 2017

On Wed, Sep 6, 2017 at 10:07 AM, Greg Ewing <greg.ewing at canterbury.ac.nz>

> Yury Selivanov wrote:
>> Greg, have you seen this new section:
>> https://www.python.org/dev/peps/pep-0550/#should-yield-from-
>> leak-context-changes
> That section seems to be addressing the idea of a generator
> behaving differently depending on whether you use yield-from
> on it.

​Regarding this, I think yield from should have the same semantics as
iterating over the generator with next/send, and PEP 555 has no issues with

> I never suggested that, and I'm still not suggesting it.
> The bottomline is that it's easier to
>> reason about context when it's guaranteed that context changes are
>> always isolated in generators no matter what.
> I don't see a lot of value in trying to automagically
> isolate changes to global state *only* in generators.
> Under PEP 550, if you want to e.g. change the decimal
> context temporarily in a non-generator function, you're
> still going to have to protect those changes using a
> with-statement or something equivalent. I don't see
> why the same thing shouldn't apply to generators.
> ​​
> It seems to me that it will be *more* confusing to give
> generators this magical ability to avoid with-statements.
> ​​
​Exactly. To state it clearly: PEP 555 does not have this issue.


+ Koos Zevenhoven + http://twitter.com/k7hoven +
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