[Python-Dev] Is PEP 572 really the most effective way to solve the problems it's targeting? (original) (raw)

Ryan Gonzalez rymg19 at gmail.com
Thu Apr 26 00:23:36 EDT 2018

On April 25, 2018 11:05:04 PM Steven D'Aprano <steve at pearwood.info> wrote:

On Wed, Apr 25, 2018 at 09:36:31PM -0500, Ryan Gonzalez wrote:

I have to say I'm not overly thrilled with PEP 572...it's almost odd, because if you asked me back when I first joined this list when I was 13, I would've no doubt said YES.

I have the opposite experience: I've warmed to it the more I have read it. Before Chris had even written this PEP, there was a Python-Ideas thread asking for dedicated syntax in comprehensions alone that would have been equivalent to a binding-expression. I was rather negative about the whole thing (but no where near as negative as I've been in the past when this has come up before), until Chris pointed out that such binding-expressions have value outside of comprehensions.

[...] Now, what's the common theme here? Declarations should be separate from expressions.

Declarations and assignments are not the same thing.

Yeah, this is what happens when I write these things when tired... I meant to also mention assignments here, and anywhere else I may have used "declaration".

We've got languages that range from baggage-filled to functional to a bit of all of the above, and none of them have added assignment inside an expression.

And your claim about assignment inside expressions is only true if you ignore the languages where assignment is an expression with a return value. You know, strange and exotic languages with hardly any users or influence, like C, C++, C#, Java, Javascript, Ruby, Perl, PHP, Lisp ...

In the majority of these, however, mixing assignments into expressions is considered bad practice.

For instance:

Some of the other languages (e.g. Perl) aren't some I'd regard as positive influences...

-- Steve

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