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bpo-41559: Implement PEP 612 - Add ParamSpec and Concatenate to typing#23702

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Fidget-Spinner:pep612
Dec 24, 2020
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bpo-41559: Implement PEP 612 - Add ParamSpec and Concatenate to typing#23702
gvanrossum merged 27 commits into
python:masterfrom
Fidget-Spinner:pep612

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@Fidget-Spinner

@Fidget-Spinner Fidget-Spinner commented Dec 8, 2020 •
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Changes:

  • Add ParamSpec and Concatenate to typing.
  • Allow both in Callable
  • Allow ParamSpec in Generic
  • Treat ParamSpec as a TypeVar (add them to __parameters__ ) in:
    • typing generics
    • types.GenericAlias
  • Generics parameterized with ParamSpec and subscripted with lists should cast those lists to tuple:
    • typing.Generic
    • types.GenericAlias
  • Tests for ParamSpec
    • Test specified use cases with typing.Callable.
    • Test specified use cases with collections.abc.Callable.
    • Test user defined generics
    • TypeVar like substitution
  • Tests for Concatenate
  • Loosened Generic and GenericAlias type checks to allow for nearly anything.

Documentation will be another patch.

https://bugs.python.org/issue41559

@Fidget-Spinner Fidget-Spinner marked this pull request as ready for review December 9, 2020 16:12
gvanrossum
gvanrossum reviewed Dec 9, 2020
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I'm sorry, I didn't get to the end of this review (not by far), but I have a few comments. Main thing though is, did you look at all the examples in PEP 612? It seems that for user-defined generic classes that have a ParamSpec parameter, things like X[int, P] are actually valid.

Maybe this indirectly also answers your question: I think that the ParamSpec should be included in __parameters__.

Also, I wonder if we could do less type checking at runtime rather than trying to be strict? I desperately want typing.py to shrink, not grow... :-)

@Fidget-Spinner

Fidget-Spinner commented Dec 9, 2020

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Points taken. Sorry X[int, P] slipped my mind since I hadn't fixed __parameters__ yet.

D'oh, I just realised I answered my own question since we need __parameters__ to implement X[int, P] in the first place.

@Fidget-Spinner Fidget-Spinner marked this pull request as draft December 10, 2020 13:42
@gvanrossum

gvanrossum commented Dec 11, 2020

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Let's wait until #23060 has landed and then see what adjustments this might need.

@Fidget-Spinner Fidget-Spinner marked this pull request as ready for review December 16, 2020 09:45
@Fidget-Spinner Fidget-Spinner marked this pull request as draft December 17, 2020 15:39
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@gvanrossum

gvanrossum commented Dec 23, 2020

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Finally looking at this...

Actually I just realized PEP 612 doesn't explicitly say that ParamSpec should support TypeVar-like substitution. Maybe I over complicated things a little by allowing that in types.GenericAlias (just for collections.abc.Callable)?

Yeah, ParamSpec is super special, and you can't do anything with it that isn't explicitly mentioned in the PEP. So it's debatable whether Callable[P, int] should even have P in its __parameters__. Then again, for the simple case A = Callable[P, int] there's no reason why we couldn't allow A[[str, str]] and get Callable[[str, str], int] as the result. But type checkers wouldn't know what to do with that -- ParamSpec is a magic cookie.

So let's not worry about those clearly wrong cases.

@gvanrossum

gvanrossum commented Dec 23, 2020 •
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Sorry, submitted too soon. (UPDATE: Not, I made a mistake -- or GitHub did. :-)

gvanrossum
gvanrossum reviewed Dec 23, 2020
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Excellent work! Thanks for your perseverance. My feedback is mostly simple improvements.

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gvanrossum reviewed Dec 23, 2020
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Re: the 3.9 issues that you discovered: maybe create a PR for those first, land that in master and 3.9 branch, then merge master into this PR?

@Fidget-Spinner

Fidget-Spinner commented Dec 24, 2020 •
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Guido, thank you so much for all the time you've put into reviewing this PR! I learnt quite a bit about the typing module in the process :).

Re: the 3.9 issues that you discovered: maybe create a PR for those first, land that in master and 3.9 branch, then merge master into this PR?

Yeah I agree, I created #23915 for that. Once that one lands, I'll merge the changes in along with some of your suggestions.

@gvanrossum

gvanrossum commented Dec 24, 2020

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I think it’s ready!

@Fidget-Spinner Fidget-Spinner mentioned this pull request Dec 24, 2020
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@gvanrossum

gvanrossum commented Dec 24, 2020

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@Fidget-Spinner Let me know if you agree.

@Fidget-Spinner

Fidget-Spinner commented Dec 24, 2020

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@Fidget-Spinner Let me know if you agree.

Yes! Sorry, I thought you were going to merge it in so I was waiting too 😆 .

@gvanrossum

gvanrossum commented Dec 24, 2020

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I figured that was the case. :-)

@gvanrossum gvanrossum merged commit 73607be into python:master Dec 24, 2020
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bedevere-bot commented Dec 24, 2020

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@gvanrossum: Please replace # with GH- in the commit message next time. Thanks!

@Fidget-Spinner

Fidget-Spinner commented Dec 24, 2020

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@gvanrossum Oh dang I knew I had a hunch I missed something :/. I forgot to convert all lists to tuples in ga_new/setup_ga too (I did it only for getitem and co.). Well on the bright side, having that as a separate PR makes backporting to 3.9 easier if anything :), and anyways lists aren't valid in genericalias other than the Callable case (which we already have covered), so we won't have anything broken even without that in right now.

@Fidget-Spinner

Fidget-Spinner commented Dec 24, 2020

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I'll fix that some other time, right now I'm celebrating 🥳

@Fidget-Spinner Fidget-Spinner deleted the pep612 branch December 24, 2020 09:19
@Fidget-Spinner Fidget-Spinner mentioned this pull request Dec 30, 2020
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@Fidget-Spinner Fidget-Spinner mentioned this pull request Feb 14, 2021
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adorilson pushed a commit to adorilson/cpython that referenced this pull request Mar 13, 2021
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bpo-41559: Implement PEP 612 - Add ParamSpec and Concatenate to typing ( …
41127ae 
python#23702)
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