[Python-Dev] PEP 550 v4

Yury Selivanov yselivanov.ml at gmail.com
Wed Sep 6 19:53:06 EDT 2017

On Wed, Sep 6, 2017 at 1:39 PM, Koos Zevenhoven <k7hoven at gmail.com> wrote:
> Now this was of course a completely fictional example, and hopefully I
> didn't introduce any bugs or syntax errors other than the ones I described.
> I haven't seen code like this anywhere, but somehow we caught the problems
> anyway.

Thank you for the example, Koos.  FWIW I agree it is a "completely
fictional example".

There are two ways how we can easily adapt PEP 550 to follow your semantics:

1. Set gen.__logical_context__ to None when it is being 'yield frommmed'

2. Merge gen.__logical_context__ with the outer LC when the generator
is iterated to the end.

But I still really dislike the examples you and Greg show to us.  They
are not typical or real-world examples, they are showcases of ways to
abuse contexts.

I still think that giving Python programmers one strong rule: "context
mutation is always isolated in generators" makes it easier to reason
about the EC and write maintainable code.


More information about the Python-Dev mailing list