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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Typing: runtime-checkable protocols are broken on `main`","articleBody":"PEP-695 protocols don't work as intended:\r\n\r\nHere's the behaviour you get with protocols that use pre-PEP 695 syntax, which is correct:\r\n\r\n```pycon\r\n\u003e\u003e\u003e from typing import Protocol, runtime_checkable, TypeVar\r\n\u003e\u003e\u003e T_co = TypeVar(\"T_co\", covariant=True)\r\n\u003e\u003e\u003e @runtime_checkable\r\n... class SupportsAbsOld(Protocol[T_co]):\r\n...     def __abs__(self) -\u003e T_co:\r\n...         ...\r\n...\r\n\u003e\u003e\u003e isinstance(0, SupportsAbsOld)\r\nTrue\r\n\u003e\u003e\u003e issubclass(float, SupportsAbsOld)\r\nTrue\r\n```\r\n\r\nAnd here's the behaviour you get on `main` with protocols that use PEP 695 syntax, which is incorrect:\r\n\r\n```pycon\r\n\u003e\u003e\u003e @runtime_checkable\r\n... class SupportsAbsNew[T_co](Protocol):\r\n...     def __abs__(self) -\u003e T_co:\r\n...         ...\r\n...\r\n\u003e\u003e\u003e isinstance(0, SupportsAbsNew)\r\nFalse\r\n\u003e\u003e\u003e issubclass(float, SupportsAbsNew)\r\nTraceback (most recent call last):\r\n  File \"\u003cstdin\u003e\", line 1, in \u003cmodule\u003e\r\n  File \"C:\\Users\\alexw\\coding\\cpython\\Lib\\abc.py\", line 123, in __subclasscheck__\r\n    return _abc_subclasscheck(cls, subclass)\r\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\r\n  File \"C:\\Users\\alexw\\coding\\cpython\\Lib\\typing.py\", line 1875, in _proto_hook\r\n    raise TypeError(\"Protocols with non-method members\"\r\nTypeError: Protocols with non-method members don't support issubclass()\r\n```\r\n\r\n\u003c!-- gh-linked-prs --\u003e\r\n### Linked PRs\r\n* gh-104556\r\n* gh-104559\n\u003c!-- /gh-linked-prs --\u003e\r\n","author":{"url":"https://github.com/AlexWaygood","@type":"Person","name":"AlexWaygood"},"datePublished":"2023-05-16T15:22:30.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":23},"url":"https://github.com/104555/cpython/issues/104555"}