[Python-Dev] assignment expressions: an alternative proposal

[Yury Selivanov]

On Tue, Apr 24, 2018 at 11:07 AM, Chris Angelico <rosuav at gmail.com> wrote:
[..]

> x = 1
> if (x = 2): ...
>
> This, according to your proposal, raises SyntaxError - not because a
> comparison was wanted and an assignment was made, but because the name
> already had a value. And, even worse, this is NOT an error:

Yes, because I'm trying to think about this from a pragmatic side of
things. My question to myself: "what syntax could I use that would
prevent me from making '=' vs '==' mistake when I code?"  To me, the
answer is that I usually want to compare local variables.

When I compare to variables from outer scopes they *usually* are on
the *right* side of '=='.

>
> x = 1
> def f():
>     if (x = 2):
>         ...
>
> That's a bizarre distinction.

Chris, FWIW I'm trying to avoid using 'bizarre', 'arcane' etc with
regards to PEP 572 or any proposal, really. For example, I,
personally, find ':=' bizarre, but it's subjective and it's
unproductive to say that.

Yury