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Non-runtime_checkable subclass of a runtime_checkable Protocol allows isinstance() #132604
Description
Bug report
Bug description:
I would expect this to raise, but it passes on all versions:
from typing import runtime_checkable, Protocol
@runtime_checkable
class Foo(Protocol):
x: int
class Bar(Foo, Protocol):
y: str
isinstance(object(), Bar)Some previous discussion in #132596 (comment) . We may not want to change this behavior for compatibility reasons, but I think it's a bug so I'm at least opening the issue.
CPython versions tested on:
CPython main branch, 3.13
Operating systems tested on:
macOS
Activity
AlexWaygood commentedon Apr 16, 2025
I agree that this behaviour seems buggy. I'd be open to deprecating it, but I do think it would need a deprecation period of several versions before we could outright remove it. This behaviour has existed since Python 3.8; I feel like it's almost certain that some project somewhere will be accidentally depending on it.
gh-132604: Deprecate inherited runtime checkability of protocols (GH-…
encukou commentedon Feb 13, 2026
The PR is merged so I'll close the issue.
pythongh-132604: Deprecate inherited runtime checkability of protocols (
pythongh-132604: Deprecate inherited runtime checkability of protocols (
Merge branch 'main' into pythongh-132604-track-deprecation
gh-132604: Track deprecation related to runtime-checkable protocols (…
[3.15] gh-132604: Track deprecation related to runtime-checkable prot…
pythongh-132604: Track deprecation related to runtime-checkable proto…