[Python-Dev] PEP 572: Assignment Expressions (original) (raw)

Mike Miller python-dev at mgmiller.net
Sun Apr 22 15:46:45 EDT 2018

On 2018-04-21 19:57, Chris Angelico wrote:

Thanks for being patient.

Looks like the crux of the issue is that "with … as" binds the result of the enter function rather than the context-manager object, as it might first appear. Therefore it's not compatible with how "as" is used for direct name bindings after "import" statements or this sub-proposal. Additionally, "except Class as instance" names the instance rather than the class.

So, the "as" keyword is already operating at an intuitive level rather than idealistic perfection. Three different semantics for import/with/except, correct? This sub-proposal lines up with the import use, I believe.

Given that there are no use cases for using assignment-expressions in the import/with/except statements, and it could be documented that if one insists an extra set of parens could make it work:

 with (callable() as cm_obj) as enter_result_obj:
     pass

It doesn't feel like this issue should be a blocker.

TL;DR - Been feebly trying to make the argument that everyday "intuitive consistency" (where the expression will be used) is more important than avoiding theoretical problems. I've never seen complex with/except statements in the wild and don't expect this feature to significantly alter that.

-Mike

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