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gh-74690: Avoid a costly type check where possible in _ProtocolMeta.__subclasscheck__ #112717

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Merged
AlexWaygood merged 3 commits into from
Dec 4, 2023
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gh-74690: Avoid a costly type check where possible in _ProtocolMeta.__subclasscheck__ #112717

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gh-74690: Avoid a costly type check where possible in `_ProtocolMeta.…
AlexWaygood Dec 4, 2023
3c7eb19
Add a docstring to help future maintainers
AlexWaygood Dec 4, 2023
3975611
improve docstring
AlexWaygood Dec 4, 2023
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improve docstring
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@AlexWaygood
AlexWaygood authored Dec 4, 2023
commit 39756114cf8b14ac8a3040af5cce6bbfdb3bf83a
3 changes: 2 additions & 1 deletion Lib/typing.py
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Expand Up @@ -1795,7 +1795,8 @@ def _type_check_issubclass_arg_1(arg):
in `issubclass(arg, <protocol>)`.

In most cases, this is verified by type.__subclasscheck__.
As such, we don't perform this check unless we absolutely have to.
Checking it again unnecessarily would slow down issubclass() checks,
so, we don't perform this check unless we absolutely have to.

For various error paths, however,
we want to ensure that *this* error message is shown to the user
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