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[match-case] Fix narrowing of class pattern with union-argument. - #19517
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hauntsaninja merged 1 commit intoOct 23, 2025
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randolf-scholz
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mypy/checker.py
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| if not proposed_type_ranges: | ||
| # This is the case for `if isinstance(x, ())` which always returns False. | ||
| return UninhabitedType(), default |
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This test is actually redundant, it works just as well if we comment it out since make_simplified_union([]) returns UninhabitedType().
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randolf-scholz
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July 27, 2025 19:32
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October 22, 2025 21:16
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Diff from mypy_primer, showing the effect of this PR on open source code: spark (https://github.com/apache/spark)
- python/pyspark/ml/connect/readwrite.py:100: error: Redundant cast to "JavaEstimator[Any]" [redundant-cast]
- python/pyspark/ml/connect/readwrite.py:103: error: Redundant cast to "JavaEvaluator" [redundant-cast]
prefect (https://github.com/PrefectHQ/prefect)
- src/prefect/tasks.py:559: error: Incompatible types in assignment (expression has type "Union[int, float, list[float], None]", variable has type "list[float]") [assignment]
+ src/prefect/tasks.py:559: error: Incompatible types in assignment (expression has type "Union[float, int, list[float], None]", variable has type "list[float]") [assignment]
starlette (https://github.com/encode/starlette)
+ starlette/middleware/errors.py:176: error: Incompatible types in assignment (expression has type "Any | None", variable has type "Response") [assignment]
+ starlette/middleware/errors.py:176: error: Argument 1 has incompatible type "Request"; expected "WebSocket" [arg-type]
+ starlette/_exception_handler.py:59: error: Argument 1 has incompatible type "Request | WebSocket"; expected "WebSocket" [arg-type]
- starlette/_exception_handler.py:61: error: Argument 1 to "run_in_threadpool" has incompatible type "Callable[[Request, Exception], Response | Awaitable[Response]] | Callable[[WebSocket, Exception], Awaitable[None]]"; expected "Callable[[Request | WebSocket, Exception], Any]" [arg-type]
+ starlette/_exception_handler.py:61: error: Argument 1 to "run_in_threadpool" has incompatible type "Callable[[Request, Exception], Response | Awaitable[Response]] | Callable[[WebSocket, Exception], Awaitable[None]]"; expected "Callable[[Request | WebSocket, Exception], Any | None]" [arg-type]
hydra-zen (https://github.com/mit-ll-responsible-ai/hydra-zen)
- src/hydra_zen/wrapper/_implementations.py:933: error: Incompatible return value type (got "type[object]", expected "DataClass_ | type[DataClass_] | ListConfig | DictConfig") [return-value]
urllib3 (https://github.com/urllib3/urllib3)
+ src/urllib3/_collections.py:359: error: Redundant cast to "Iterable[tuple[str, str]]" [redundant-cast]
websockets (https://github.com/aaugustin/websockets)
+ src/websockets/legacy/protocol.py:641: error: Redundant cast to "Iterable[str | bytes | bytearray | memoryview[int]]" [redundant-cast]
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hauntsaninja
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Fixes #19468
Based on earlier PR #19473
Modified tests
New Tests