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 :
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

-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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