[Python-ideas] [Python-Dev] Language proposal: variable assignment in functional context

[Michał Żukowski]

I've implemented a PoC of `where` expression some time ago.

https://github.com/thektulu/cpython/commit/9e669d63d292a639eb6ba2ecea3ed2c0c23f2636

just compile and have fun.



2017-06-17 2:27 GMT+02:00 Steven D'Aprano <steve at pearwood.info>:

> Welcome Robert. My response below.
>
> Follow-ups to Python-Ideas, thanks. You'll need to subscribe to see any
> further discussion.
>
>
> On Fri, Jun 16, 2017 at 11:32:19AM +0000, Robert Vanden Eynde wrote:
>
> > In a nutshell, I would like to be able to write:
> > y = (b+2 for b = a + 1)
>
> I think this is somewhat similar to a suggestion of Nick Coghlan's. One
> possible syntax as a statement might be:
>
> y = b + 2 given:
>     b = a + 1
>
>
> https://www.python.org/dev/peps/pep-3150/
>
> In mathematics, I might write:
>
> y = b + 2 where b = a + 1
>
> although of course I wouldn't do so for anything so simple. Here's a
> better example, the quadratic formula:
>
>       -b ± √Δ
> x =  ─────────
>          2a
>
> where Δ = b² - 4ac
>
> although even there I'd usually write Δ in place.
>
>
> > Python already have the "functional if", lambdas, list comprehension,
> > but not simple assignment functional style.
>
> I think you mean "if *expression*" rather than "functional if". The term
> "functional" in programming usually refers to a particular paradigm:
>
> https://en.wikipedia.org/wiki/Functional_programming
>
>
> --
> Steve
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