[3.9] bpo-42195: Override _CallableGenericAlias's __getitem__ (GH-23915) by miss-islington · Pull Request #23916 · python/cpython
Added __getitem__ for _CallableGenericAlias so that it returns a subclass (itself) of types.GenericAlias rather than the default behavior of returning a plain types.GenericAlias. This fixes repr issues occuring after TypeVar substitution arising from the previous behavior.
(cherry picked from commit 6dd3da3)
Co-authored-by: kj 28750310+Fidget-Spinner@users.noreply.github.com