Reuse stdlib PEP 593 implementation in typing_extensions if present #699
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Following [1] this prevents multiple runtime implementations of Annotated and get_type_hints from existing on Python 3.9 (which has recently merged PEP 593 changes[2]). Reexporting allows code targetting both Python pre-3.9 and 3.9+ to be able to import from typing_extensions and to keep working without changes. [1] python/cpython#18260 (comment) [2] python/cpython#18260
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Following [1] this prevents multiple runtime implementations of Annotated
and get_type_hints from existing on Python 3.9 (which has recently
merged PEP 593 changes[2]). Reexporting allows code targetting both
Python pre-3.9 and 3.9+ to be able to import from typing_extensions and
to keep working without changes.
_AnnotatedAliasimport is needed for #698 to work.[1] python/cpython#18260 (comment)
[2] python/cpython#18260