[Python-Dev] Scope issues [was: Alternative forms [was: PEP 463: Exception-catching expressions]]

[Jim J. Jewett]

On Fri Mar 7 20:54:31 CET 2014, Chris Angelico wrote:
> On Sat, Mar 8, 2014 at 5:58 AM, Jim J. Jewett <jimjjewett at gmail.com> wrote:
>> (Thu Mar 6 23:26:47 CET 2014) Chris Angelico responded:

>>> ...[as-capturing is] deferred until there's a non-closure means of
>>> creating a sub-scope.

>> The problem is that once it is deployed as leaking into the parent
>> scope, backwards compatibility may force it to always leak into
>> the parent scope.  (You could document the leakage as a bug or as
>> implementation-defined, but ... those choices are also sub-optimal.)

> It'll never be deployed as leaking, for the same reason that the
> current 'except' statement doesn't leak:

I don't think that is the full extent of the problem.  From Nick's
description, this is a nasty enough corner case that there may
be glitches no one notices in time.

The PEP should therefore explicitly state that implementation details
may force the deferral to be permanent, and that this is considered an
acceptable trade-off.
        

-jJ

--

Sorry for the botched subject line on the last previous message.
If there are still threading problems with my replies, please
email me with details, so that I can try to resolve them.  -jJ