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GeezerVison is showing github.com — bpo-43224: Implement substitution of unpacked TypeVarTuple by serhiy-storchaka · Pull Request #31800 · python/cpython

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@serhiy-storchaka

@serhiy-storchaka serhiy-storchaka commented Mar 10, 2022 •
edited by bedevere-bot
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https://bugs.python.org/issue43224

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@serhiy-storchaka
serhiy-storchaka requested review from Fidget-Spinner, JelleZijlstra and gvanrossum as code owners March 10, 2022 18:54
@bedevere-bot bedevere-bot added the awaiting core review label Mar 10, 2022
@the-knights-who-say-ni the-knights-who-say-ni added the CLA signed label Mar 10, 2022
@serhiy-storchaka
bpo-43224: Implement substitution of unpacked TypeVarTuple
4fab260
@serhiy-storchaka
serhiy-storchaka force-pushed the typevartuple-subst branch from da60f24 to 4fab260 Compare March 10, 2022 18:55
mrahtz
mrahtz reviewed Mar 10, 2022
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Comment thread Lib/typing.py Outdated
raise NotImplementedError(
"Type substitution for TypeVarTuples is not yet implemented"
)
if len(self.__parameters__) == 1 and isinstance(self.__parameters__[0], TypeVarTuple):

@mrahtz mrahtz Mar 10, 2022

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I'm not sure it's sufficient to only check for the case where len(self.__parameters__) == 1 - we could have e.g.:

T1 = TypeVar('T1')
T2 = TypeVar('T2')
Ts = TypeVarTuple('Ts')
class A(Generic[T1, T2, Unpack[Ts]]): pass
B = A[int, T2, Unpack[Ts]]
C = B[str, float]
print(C)

There, B.__parameters__ is (T2, Ts), causing a TypeError later on in the code.

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@serhiy-storchaka serhiy-storchaka Mar 11, 2022

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You are right. The previous code only worked with existing tests. New code adds tests for generics with multiple type variables.

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@mrahtz

mrahtz commented Mar 10, 2022

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Thanks for looking into this!
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This was referenced Mar 10, 2022
bpo-43224: Implement PEP 646 changes to typing.py #31021
Merged
bpo-43224: Work around substitution of unpacked TypeVarTuple #31804
Closed
serhiy-storchaka added 4 commits March 11, 2022 09:53
@serhiy-storchaka
Support multiple type variables
8a8cf5d
@serhiy-storchaka
Add tests for Tuple.
a376210
@serhiy-storchaka
Merge branch 'main' into typevartuple-subst
b0412ec
@serhiy-storchaka
Simplify.
425d779
@serhiy-storchaka serhiy-storchaka added the skip news label Mar 11, 2022
@serhiy-storchaka
serhiy-storchaka merged commit 5b1b9ea into python:main Mar 11, 2022
@bedevere-bot bedevere-bot removed the awaiting core review label Mar 11, 2022
@serhiy-storchaka
serhiy-storchaka deleted the typevartuple-subst branch March 11, 2022 19:44
@JelleZijlstra JelleZijlstra mentioned this pull request Mar 11, 2022
bpo-43224: Implement substitution of unpacked TypeVarTuple in C #31828
Merged
@mrahtz

mrahtz commented Mar 12, 2022

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Woah, I'm not sure merging this was a good idea. We discussed this extensively in #31021 (review) and decided against implementing it this way. There are too many edge cases (e.g. the merged implementation will happily assign an unpacked arbitrary-length tuple such as *tuple[int, ...] to a plain TypeVar, which is not legal - see the extensive tests in b9b1c80#diff-04d29c98076c2d6bb75921ea9becb26a862544d39b71db87b6e354c759b9305dL794), and @JelleZijlstra suspected it might cause issues with Annotated.

I'd strongly prefer this merge to be reversed in favour of #31804 and/or further discussion on what the right approach is.
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@serhiy-storchaka

serhiy-storchaka commented Mar 12, 2022

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I think that list[T][int] should return list[int], and tuple[*Ts][int, str] should return tuple[int, str].

Workaround can be used in cases where this does not work.
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@mrahtz

mrahtz commented Mar 13, 2022

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If you're adamant about keeping this implementation, I don't feel happy about it, but I don't want this to become a blocker for us. I'll submit a new PR with extra test cases so we can be more confident we've covered the edge cases.
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@mrahtz mrahtz mentioned this pull request Mar 13, 2022
bpo-43224: Add more tests for typevar substitution #31844
Closed
@mrahtz mrahtz mannequin mentioned this pull request Apr 11, 2022
Add support for PEP 646 #87390
Closed
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Reviewers

@gvanrossum gvanrossum Awaiting requested review from gvanrossum
@Fidget-Spinner Fidget-Spinner Awaiting requested review from Fidget-Spinner
@JelleZijlstra JelleZijlstra Awaiting requested review from JelleZijlstra JelleZijlstra is a code owner
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@mrahtz mrahtz mrahtz left review comments
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@serhiy-storchaka @mrahtz @the-knights-who-say-ni @bedevere-bot
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