Concatenate implementation generates runtime exception if parameterized by ... #48

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1. Fidget-Spinner commented on Jul 7, 2022

   

   Fidget-Spinner

   on Jul 7, 2022

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   This seems like a bug in Python's typing module itself.

   # In 3.9
   typing.Callable[T, int][...]
   
   TypeError: Parameters to generic types must be types. Got Ellipsis.

   The problem is that Callable uses the default _GenericAlias's substitution behavior pre 3.10. Which means its checks are too restrictive. We had to intentionally loosen the checks in 3.10 to get around this.

   I don't think we can fix this from typing_extensions unless we monkey patch typing._GenericAlias.__getitem__ (or typing._type_check). I don't feel too good doing that though.
2. Fidget-Spinner commented on Jul 7, 2022

   

   Fidget-Spinner

   on Jul 7, 2022

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   Also, we're sadly past the stage for bugfixes in 3.9. I suggest that we add this to the known limitations in the README and (unfortunately) close as can't fix.
3. JelleZijlstra commented on May 22, 2023

   

   JelleZijlstra

   on May 22, 2023

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   This is now documented as a limitation at https://typing-extensions.readthedocs.io/en/latest/#Concatenate. If there is a reasonable way to fix it, I'd accept a PR.
4. AlexWaygood

   added

   pep-612

   on Feb 22, 2024
5. Daraan commented on Oct 3, 2024

   

   Daraan

   on Oct 3, 2024

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   I am currently looking at this again and the statement that "It runs fine on Python 3.10 if using typing.Concatenate" confused be a bit.
   In hindsight this should only hold for 3.10.0-3.10.2 afterwards it also does not run on the other 3.10 typing versions either.

   Edit: Monkey patching copy_with of _ConcatenateGenericAlias to the 3.11 variant would be sufficient for the 3.10 versions.
   Edit2: Also doable without monkey patch in 3.10.
6. JelleZijlstra

   closed this as completedin #479on Oct 21, 2024
7. Daraan commented on Oct 22, 2024

   

   Daraan

   on Oct 22, 2024

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   As a summary:

   #479 covered this Issue only for 3.10, or rather 3.10.3+.

   For 3.8 & 3.9 I see no other way around monkey patching typing._GenericAlias.__getitem__ to fix this issue.
   The essential part of the monkey patch could be similar to this, maybe with more checks on the origin:

   - params = tuple(_type_check(p, msg) for p in params)
   + params = tuple(typing._type_check(p, msg) if p is not ... else ...
   +                       for p in params)