[Python-Dev] PEP 572: Assignment Expressions

[Paul Moore]

On 17 April 2018 at 14:07, Paul Moore <p.f.moore at gmail.com> wrote:
> On 17 April 2018 at 14:01, David Mertz <mertz at gnosis.cx> wrote:
>> Strongly agree with Nick that only simple name targets should be permitted
>> (at least initially). NONE of the motivating cases use more complex targets,
>> and allowing them encourages obscurity and code golf.
>
> I also agree. Originally I would have said why not allow them, it's a
> potentially useful generalisation. But Nick's examples pretty clearly
> demonstrate that there are a lot of unclear edge cases involved, and
> even though "prevent people writing ugly code" is explicitly stated as
> a non-goal in the PEP, that doesn't mean it's OK to allow an obvious
> bug magnet with no clear use cases.

I should also point out that I remain -0 on this proposal (I'd already
said this on python-ideas, but I should probably repeat it here). For
me, the use cases are mostly marginal, and the major disadvantage is
in having two forms of assignment. Explaining to a beginner why we use
a := b in an expression, but a = b in a statement is going to be a
challenge.

The fact that the PEP needs a section covering all the style guide
warnings we feel are needed seems like it's a warning bell, too.

Paul