typing.Annotated[int, ...] is subclassable
#96771
Comments
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Related: #96080 |
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But, Python 3.10.0 (default, Nov 1 2021, 10:24:06) [Clang 11.0.0 (clang-1100.0.33.16)] on darwin
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>>> import typing
>>> class Some(typing.Annotated[int, 'meta']): ...
...
>>> Some.__mro__
(<class '__main__.Some'>, <class 'int'>, <class 'object'>) |
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Looks like there's a test for quite the opposite: https://github.com/python/cpython/blame/53a54b781d1f05f2d0b40ce88b3da92d5d23e9d2/Lib/test/test_typing.py#L6713-L6717 It ensures that |
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I disagree that it is a bug that you can subclass SpecialInt: TypeAlias = Annotated[int, "very special"]
class Foo(SpecialInt): ...This works fine, and I don't see why the cases should be treated differently: SpecialInt: TypeAlias = int
class Foo(SpecialInt): ... |
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In any case, it would surely be backwards-incompatible to change this behaviour now? |
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Yes, changing this will be backward incompatible. Even type-checkers can understand this: from typing import Annotated
class Some(Annotated[int, 'meta']):
pass
reveal_type(Some)
# ex.py:6: note: Revealed type is "Overload(def (Union[builtins.str, builtins.bytes, array.array[Any], mmap.mmap, ctypes._CData, pickle.PickleBuffer, typing.SupportsInt, typing_extensions.SupportsIndex, _typeshed.SupportsTrunc] =) -> ex.Some, def (Union[builtins.str, builtins.bytes], base: typing_extensions.SupportsIndex) -> ex.Some)"So, it probably should stay as-is. |
You can subclass
Annotated[int, "meta"]:But, here are a couple of problems:
Annotatedin the first placeAnnotatedcannot be subclassed: https://github.com/python/cpython/blame/53a54b781d1f05f2d0b40ce88b3da92d5d23e9d2/Lib/test/test_typing.py#L6562-L6565 hereI think that
Annotatedshould not be subclasses and this is a bug.The PR is incoming :)
I found this while working on #96769
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