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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Fri, 11 Sep 2015 10:27:57 -0600
Subject: Re: Python handles globals badly.
To: Python <python-list@python.org>
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Xref: csiph.com comp.lang.python:96356

On Fri, Sep 11, 2015 at 10:04 AM, Chris Angelico <rosuav@gmail.com> wrote:
> On Sat, Sep 12, 2015 at 1:57 AM,  <random832@fastmail.us> wrote:
>> On Fri, Sep 11, 2015, at 11:55, Chris Angelico wrote:
>>> On Sat, Sep 12, 2015 at 1:49 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
>>> > Ah, that makes sense. It's writing into the dict that is created and
>>> > returned by locals(), but not actually updating the frame locals which
>>> > are the source of truth.
>>>
>>> Yeah... but it only makes sense to people who understand the
>>> implementation. It's certainly not a logical and sane behaviour that
>>> would be worth documenting and using.
>>
>> What else would you document? Reading from them is a reasonable thing to
>> do, and works. Writing to them is a reasonable thing to want to do, but
>> won't work, so you need to document that it doesn't work.
>
> Documenting that "it doesn't work" seems fine. Documenting the
> specific behaviour (that it gives you a sort of "shadow" locals, into
> which you can write, but which won't persist past the execution of
> that block of code) seems pointless. Especially since this behaviour
> is implementation-dependent anyway.

It's documented in the standard library docs:
https://docs.python.org/3.4/library/functions.html#exec

I think that's probably sufficient.