[Python-Dev] Pep 550 and None/masking (original) (raw)

Yury Selivanov yselivanov.ml at gmail.com
Mon Aug 28 11:50:04 EDT 2017

On Sun, Aug 27, 2017 at 4:01 PM, Nathaniel Smith <njs at pobox.com> wrote:

I believe that the current status is:

- assigning None isn't treated specially – it does mask any underlying values (which I think is what we want)

Correct.

- there is currently no way to "unmask" - but it's generally agreed that there should be a way to do that, at least in some cases, to handle the save/restore issue I raised. It's just that Yury & Elvis wanted to deal with restructuring the PEP first before doing more work on the api details.

Yes. I think it's a good time to start a discussion about this, I can list a couple ideas here.

For checking if a context variable has a value in the topmost LC, we can add two new keyword arguments to the "ContextVar.lookup()" method:

ContextVar.lookup(*, default=None, topmost=False)

If topmost is set to True, lookup will only check the topmost LC.

For deleting a value from the topmost LC we can add a new "ContextVar.delete()" method.

Yury

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