[Python-Dev] Informal educator feedback on PEP 572 (was Re: 2018 Python Language Summit coverage, last part)

Ivan Pozdeev vano at mail.mipt.ru
Wed Jun 27 20:10:40 EDT 2018

On 28.06.2018 2:31, Greg Ewing wrote:
> Steven D'Aprano wrote:
>> The *very first* motivating example for this proposal came from a 
>> comprehension.
>> I think it is both unfortunate and inevitable that the discussion bogged
>> down in comprehension-hell.
> I think the unfortunateness started when we crossed over from
> talking about binding a temporary name for use *within* a
> comprehension or expression, to binding a name for use *outside*
> the comprehension or expression where it's bound.
I've shown in <05f368c2-3cd2-d7e0-9f91-27afb40d5b35 at mail.mipt.ru> (27 
Jun 2018 17:07:24 +0300) that assignment expressions are fine in most 
use cases without any changes to scoping whatsoever.

So, as Guido suggested in 
<CAP7+vJ+xBAT4ZvAo4B7qSqxnnpj8jJ1VZ-Le7EwT8=n-UTjE3Q at mail.gmail.com> (26 
Jun 2018 19:36:14 -0700), the scoping matter can be split into a 
separate PEP and discussion.

> As long as it's for internal use, whether it's in a comprehension
> or not isn't an issue.
>> Tim Peters has also given a couple of good examples of mathematical 
>> code that would benefit strongly from this feature.
>> Going back a few months now, they were the examples that tipped me over
> Well, I remain profoundly unconvinced that writing comprehensions
> with side effects is ever a good idea, and Tim's examples did
> nothing to change that.


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