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bpo-44791: Fix substitution of ParamSpec in Concatenate with differen… - #27518

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serhiy-storchaka:typing-concatenate-subst
Jan 27, 2022
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bpo-44791: Fix substitution of ParamSpec in Concatenate with differen…#27518
serhiy-storchaka merged 5 commits into
python:mainfrom
serhiy-storchaka:typing-concatenate-subst

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@serhiy-storchaka

@serhiy-storchakaserhiy-storchaka commented Jul 31, 2021•
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…t parameter expressions

https://bugs.python.org/issue44791

@serhiy-storchakaserhiy-storchaka added type-bug An unexpected behavior, bug, or error needs backport to 3.10 only security fixes labels Jul 31, 2021
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This PR is stale because it has been open for 30 days with no activity.

@github-actionsgithub-actionsBot added the stale Stale PR or inactive for long period of time. label Aug 31, 2021
@Fidget-Spinner

Fidget-Spinner commented Aug 31, 2021•
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Sorry, I'd forgotten about this. Last I recall we need to amend PEP 612 right? Serhiy would you like me to try write an initial draft (and then you can review it?).

@serhiy-storchaka

serhiy-storchaka commented Aug 31, 2021

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Sure.

What should be clarified:

ParamSpec variables and TypeVar variables are exposed in __parameters__, in order of occurrence. Give examples of Callable and user-defined generics.
Generic types with non-empty __parameters__ are indexable. TypeVar variables can only be substituted with a type expression (type or TypeVar). ParamSpec variables can only be substituted with parameters_expression.
Specifies results of substituting Callable with every of four kinds of parameters_expression.
Specifies results of substituting user-defined generic with every of four kinds of parameters_expression.
Specifies results of substituting ParamSpec in Concatenate.
Substitution ParamSpec with a list of types can lead to __args__ containing list of types. Specify that variables are substituted in lists in __args__.

serhiy-storchaka
serhiy-storchaka commented Aug 31, 2021
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Comment threadLib/test/test_typing.py Outdated
self.assertEqual(C[int, P2], Concatenate[int, P2])
self.assertEqual(C[int, [str, float]], (int, str, float))
self.assertEqual(C[int, []], (int,))
self.assertEqual(C[int, ...], Concatenate[int, ...])

@serhiy-storchakaserhiy-storchakaAug 31, 2021

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I am not sure about this. It can be just [int, ...], although it would create a discrepancy with using ellipsis in Tuple.

@github-actionsgithub-actionsBot removed the stale Stale PR or inactive for long period of time. label Sep 1, 2021
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serhiy-storchaka marked this pull request as ready for review January 27, 2022 12:30
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serhiy-storchaka merged commit ecfacc3 into python:mainJan 27, 2022
@miss-islington

miss-islington commented Jan 27, 2022

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Thanks @serhiy-storchaka for the PR 🌮🎉.. I'm working now to backport this PR to: 3.10.
🐍🍒⛏🤖

miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Jan 27, 2022
@serhiy-storchaka@miss-islington
bpo-44791: Fix substitution of ParamSpec in Concatenate with differen…
feb78c0
…t parameter expressions (pythonGH-27518)
* Substitution with a list of types returns now a tuple of types.
* Substitution with Concatenate returns now a Concatenate with
concatenated lists of arguments.
* Substitution with Ellipsis is not supported.
(cherry picked from commit ecfacc3)
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
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bedevere-bot commented Jan 27, 2022

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GH-30959 is a backport of this pull request to the 3.10 branch.

@bedevere-botbedevere-bot removed the needs backport to 3.10 only security fixes label Jan 27, 2022
@serhiy-storchaka
serhiy-storchaka deleted the typing-concatenate-subst branch January 27, 2022 12:35
miss-islington added a commit that referenced this pull request Jan 27, 2022
@miss-islington@serhiy-storchaka
bpo-44791: Fix substitution of ParamSpec in Concatenate with differen…
89db090
…t parameter expressions (GH-27518)
* Substitution with a list of types returns now a tuple of types.
* Substitution with Concatenate returns now a Concatenate with
concatenated lists of arguments.
* Substitution with Ellipsis is not supported.
(cherry picked from commit ecfacc3)
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
@gvanrossum

gvanrossum commented Jan 27, 2022

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Should this be backported?

@serhiy-storchaka

serhiy-storchaka commented Jan 27, 2022

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This PR fixes substitution of a ParamSpec variable with a Concatenate or a list of types. It is not specified by PEP 612, but does not conflict with it.

Substitution with an ellipsis is now an error, because the result cannot be expressed without changing PEP 612. I have opened #30969 for supporting ellipsis.

@positaposita mentioned this pull request Feb 26, 2022
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@serhiy-storchakaserhiy-storchaka mentioned this pull request Apr 29, 2022
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