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[Python-ideas] PEP draft: context variables

Nathaniel Smith njs at pobox.com
Mon Sep 4 20:49:56 EDT 2017 
On Mon, Sep 4, 2017 at 2:50 PM, Koos Zevenhoven <k7hoven at gmail.com> wrote:
> Hi all,
>
> as promised, here is a draft PEP for context variable semantics and
> implementation. Apologies for the slight delay; I had a not-so-minor
> autosave accident and had to retype the majority of this first draft.
>
> During the past years, there has been growing interest in something like
> task-local storage or async-local storage. This PEP proposes an alternative
> approach to solving the problems that are typically stated as motivation for
> such concepts.

>From a quick skim, my impression is:

All the high-level semantics you suggest make sense... in fact, AFAICT
they're exactly the same semantics we've been using as a litmus test
for PEP 550. I think PEP 550 is sufficient to allow implementing all
your proposed APIs (and that if it isn't, that's a bug in PEP 550).

OTOH, your proposal doesn't provide any way to implement functions
like decimal.setcontext or numpy.seterr, except by pushing a new state
and never popping it, which leaks memory and permanently increases the
N in the O(N) lookups.

I didn't see any direct comparison with PEP 550 in your text (maybe I
missed it). Why do you think this approach would be better than what's
in PEP 550?

-n

-- 
Nathaniel J. Smith -- https://vorpus.org
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