Thanks for taking the time to write this PEP, Chris, even though I'm -1 on the idea. I'm glad to just have this as a historical document for the idea.

On Tue, 27 Feb 2018 at 22:53 Chris Angelico <rosuav@gmail.com> wrote:
On Wed, Feb 28, 2018 at 4:52 PM, Robert Vanden Eynde
<robertve92@gmail.com> wrote:
> Hello Chris and Rob,
>
> did you compare your proposal tothe subject called "[Python-ideas] Temporary
> variables in comprehensions" on this month list ?

Yes, I did; that's one of many threads on the subject, and is part of
why I'm writing this up.

One section that I have yet to write is "alternative syntax
proposals", which is where I'd collect all of those together.

> If you don't want to go through all the mails, I tried to summarize the
> ideas in this mail :
> https://mail.python.org/pipermail/python-ideas/2018-February/048987.html
>
> In a nutshell one of the proposed syntax was
>
> stuff = [(y, y) where y = f(x) for x in range(5)]
>
> Or with your choice of keyword,
>
> stuff = [(y, y) with y = f(x) for x in range(5)]
>
> Your proposal uses the *reverse* syntax :
>
> stuff = [(y, y) with f(x) as y for x in range (5)]
> ...
> I wish I could write a pep to summarize all the discussions (including
> yours, my summary, including real world examples, including pro's and
> con's), or should I do a gist on GitHub so that we can talk in a more "forum
> like" manner where people can edit their answers and modify the document ?
> This mailing is driving me a bit crazy.

This is exactly why I am writing up a PEP. Ultimately, it should list
every viable proposal (or group of similar proposals), with the
arguments for and against. Contributions of actual paragraphs of text
are VERY welcome; simply pointing out "hey, don't forget this one" is
also welcome, but I then have to go and write something up, so it'll
take a bit longer :)

> As Rob pointed out, your syntax "(f(x) as y, y)" is really assymmetric and
> "(y, y) with f(x) as y" or "(y, y) with y = f(x)" is probably prefered.
> Moreover I agree with you the choice of "with" keyword could be confused
> with the "with f(x) as x:" statement in context management, so maybe "with x
> = f(x)" would cleary makes it different ? Or using a new keyword like "where
> y = f(x)", "let y = f(x)" or probably better "given y = f(x)", "given" isn't
> used in current librairies like numpy.where or sql alchemy "where".

And also the standard library's tkinter.dnd.Icon, according to a quick
'git grep'; but that might be just an example, rather than actually
being covered by backward-compatibility guarantees. I think "given" is
the strongest contender of the three, but I'm just mentioning all
three together.

A new version of the PEP has been pushed, and should be live within a
few minutes.

https://www.python.org/dev/peps/pep-0572/

Whatever I've missed, do please let me know. This document should end
up incorporating, or at least mentioning, all of the proposals you
cited.

ChrisA
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