On Sun, Jun 24, 2018 at 11:50 AM Steven D'Aprano <steve@pearwood.info> wrote:
> [...] IIRC (b) originated with Tim.

I'm not sure who came up with the idea first, but as I remember it, the
first mention of this came in a separate thread on Python-Ideas:


so possibly I'm to blame :-)

Actually that post sounds like the OP of that thread (Peter O'Connor) is to blame --  he proposed a similar thing using `=` for the assignment and custom syntax (`from <value>`) to specify the initial value, and it looks like that inspired you.
> But his essay on the topic, included as Appendix A (
> https://www.python.org/dev/peps/pep-0572/#appendix-a-tim-peters-s-findings)
> does not even mention comprehensions. However, he did post his motivation
> for (b) on python-ideas, IIRC a bit before PyCon; and the main text of the
> PEP gives a strong motivation (
> https://www.python.org/dev/peps/pep-0572/#scope-of-the-target).
> Nevertheless, maybe we should compromise and drop (b)?

I will have more to say about the whole "comprehensions are their own
scope" issue later. But I'd like to see Nick's proposed PEP, or at least
a draft of it, before making any final decisions.

Agreed, though I assume it's just `given` again.
If it came down to it, I'd be happy with the ability to declare an
assignment target nonlocal in the comprehension if that's what it takes.
What do you think of this syntax?

    [global|nonlocal] simple_target := expression

Inside a comprehension, without a declaration, the target would be
sublocal (comprehension scope); that should make Nick happier :-)

It's more special syntax. Just taking part (a) of PEP 572 would make most people happy enough.
--Guido van Rossum (python.org/~guido)