[Python-Dev] assignment expressions: an alternative proposal (original) (raw)

Yury Selivanov yselivanov.ml at gmail.com
Tue Apr 24 11:19:27 EDT 2018

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

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