[Python-ideas] PEP 572: Statement-Local Name Bindings

[Brett Cannon]

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 I'm glad to just have this as a historical document for the idea.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 at gmail.com> wrote:

> On Wed, Feb 28, 2018 at 4:52 PM, Robert Vanden Eynde
> <robertve92 at 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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