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Use contravariant type variable rather than object in Container #15320

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Merged
srittau merged 5 commits into from
Jan 24, 2026
Merged

Use contravariant type variable rather than object in Container #15320

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53675b6
use 'Any' rather than object in Container
randolf-scholz Jan 24, 2026
2602adc
use contravariant typevar
randolf-scholz Jan 24, 2026
09a0f41
add comment for Container[Any] usage in Collection
randolf-scholz Jan 24, 2026
7201649
make _T_contra default to Any
randolf-scholz Jan 24, 2026
45ebd8a
renamed type var and restored crucial comment
randolf-scholz Jan 24, 2026
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9 changes: 6 additions & 3 deletions stdlib/typing.pyi
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Original file line number Diff line number Diff line change
Expand Up @@ -640,14 +640,17 @@ class AsyncGenerator(AsyncIterator[_YieldT_co], Protocol[_YieldT_co, _SendT_cont
) -> Coroutine[Any, Any, _YieldT_co]: ...
def aclose(self) -> Coroutine[Any, Any, None]: ...

_ContainerT_contra = TypeVar("_ContainerT_contra", contravariant=True, default=Any)

@runtime_checkable
class Container(Protocol[_T_co]):
class Container(Protocol[_ContainerT_contra]):
# This is generic more on vibes than anything else
@abstractmethod
def __contains__(self, x: object, /) -> bool: ...
def __contains__(self, x: _ContainerT_contra, /) -> bool: ...

@runtime_checkable
class Collection(Iterable[_T_co], Container[_T_co], Protocol[_T_co]):
class Collection(Iterable[_T_co], Container[Any], Protocol[_T_co]):
# Note: need to use Container[Any] instead of Container[_T_co] to ensure covariance.
# Implement Sized (but don't have it as a base class).
@abstractmethod
def __len__(self) -> int: ...
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