Description

JelleZijlstra

opened on May 19, 2023

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Previously typing.TypeVar could be subclassed, and typing_extensions actually does this. However, the new C implementation of TypeVar doesn't allow subclassing. For compatibility, let's restore the ability to subclass it.

Reacted by Alex Waygood and Carl Meyer

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1. JelleZijlstra

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   topic-typing

   on May 19, 2023
2. JelleZijlstra

   self-assigned this

   on May 19, 2023
3. JelleZijlstra commented on May 19, 2023

   

   JelleZijlstra

   on May 19, 2023

   MemberAuthor

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   Looking more at the previous implementation, it wasn't actually subclassable normally, only if you passed the special _root=True argument to __init_subclass__:

   cpython/Lib/typing.py

   Line 397 in 702ce87

   def __init_subclass__(cls, /, *args, **kwds):

   That was an explicitly private API, so I don't think we need to preserve this behavior in C.

   Reacted by Alex Waygood
4. JelleZijlstra commented on May 20, 2023

   

   JelleZijlstra

   on May 20, 2023

   MemberAuthor

   More actions

   Alternative solution in python/typing_extensions#162.
5. JelleZijlstra

   closed this as not plannedon May 20, 2023

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