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gh-132604: Deprecate inherited runtime checkability of protocols - #143806

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encukou merged 21 commits into
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johnslavik:deprecate-inherited-runtime-protocols
Feb 9, 2026
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gh-132604: Deprecate inherited runtime checkability of protocols#143806
encukou merged 21 commits into
python:mainfrom
johnslavik:deprecate-inherited-runtime-protocols

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@johnslavikjohnslavik commented Jan 13, 2026•
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I've chosen to go ahead with a 5-year deprecation period as Alex told me he'd do at least (thx!).
If this deprecation is too problematic, we can raise the warning eternally / soft deprecate -- and never eventually raise an exception.

📚 Documentation preview 📚: https://cpython-previews--143806.org.readthedocs.build/

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Deprecate inherited runtime checkability of protocols
521a6a5
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Add tests
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No members are added to protocol classes to simplify testing. `issubclass` can only check method members.
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Document runtime-checkability on protocols
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Add news entry
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johnslavik marked this pull request as ready for review January 13, 2026 16:08
JelleZijlstra
JelleZijlstra reviewed Jan 19, 2026
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Thanks!

Comment threadDoc/library/typing.rst Outdated
Comment threadLib/typing.py Outdated
Comment threadMisc/NEWS.d/next/Library/2026-01-13-15-56-03.gh-issue-132604.lvjNTr.rst Outdated
Comment threadLib/typing.py Outdated
johnslavik
johnslavik commented Jan 19, 2026
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johnslavikand others added 2 commits January 19, 2026 16:55
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Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
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Change flag name to `__typing_is_deprecated_inherited_runtime_protoco…
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…l__`
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
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johnslavik commented Jan 19, 2026•
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I think we can use :deco: for runtime_checkable so I'll do that.
EDIT: Sphinx is a little limited with the markup in this regard; I've applied :deco: in the news entry and that's it.

johnslavikand others added 2 commits January 19, 2026 17:54
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Reword news entry
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Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
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Update test message re to match
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Comment threadMisc/NEWS.d/next/Library/2026-01-13-15-56-03.gh-issue-132604.lvjNTr.rst
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johnslavik commented Jan 23, 2026

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Merging main to fix CI.

@encukou

encukou commented Feb 4, 2026

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I'll merge on Friday if there are no objections.

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encukou merged commit ff531f9 into python:mainFeb 9, 2026
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encukou commented Feb 9, 2026

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Almost Friday :)

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johnslavik deleted the deprecate-inherited-runtime-protocols branch February 13, 2026 15:02
thunder-coding pushed a commit to thunder-coding/cpython that referenced this pull request Feb 15, 2026
@johnslavik@JelleZijlstra@thunder-coding
pythongh-132604: Deprecate inherited runtime checkability of protocols (
fb47c4d
pythonGH-143806)
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
ljfp pushed a commit to ljfp/cpython that referenced this pull request Apr 25, 2026
@johnslavik@JelleZijlstra@ljfp
pythongh-132604: Deprecate inherited runtime checkability of protocols (
ee0f59d
pythonGH-143806)
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
@johnslavikjohnslavik mentioned this pull request Jul 27, 2026
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@JelleZijlstraJelleZijlstraJelleZijlstra approved these changes
@AlexWaygoodAlexWaygoodAwaiting requested review from AlexWaygoodAlexWaygood is a code owner

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