[Python-Dev] assignment expressions: an alternative proposal

[Chris Angelico]

On Wed, Apr 25, 2018 at 2:23 AM, Steven D'Aprano <steve at pearwood.info> wrote:
> On Tue, Apr 24, 2018 at 11:25:58AM -0400, Yury Selivanov wrote:
>
>> No, it doesn't. The check is performed during compile phase, and
>> Python does not unroll loops. Anyways, read below.
>
> What does unrolling loops have to do with anything? And besides, loop
> unrolling is an implementation detail -- maybe Python will unroll loops,
> maybe it won't.
>
> If you insist that the check is only done at compile time, then your
> description is wrong and your rule that "it is *not* allowed to mask
> names in the current local scope" is false. It *is* allowed to shadow
> names in the local scope, but only names that cannot be determined at
> compile-time.
>
>     from math import *
>     process(arg, (pi = 1), pi+1)  # allowed
>
> That's more and worse complexity.

That's not allowed at local scope (at least, it's not allowed at
function scope - is there any other "local scope" at which it is
allowed?). Not sure if you can craft equivalent shenanigans with
'exec'.

ChrisA