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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Untested code in `typing.py`","articleBody":"# Bug report\r\n\r\nIf you apply this diff to `typing.py`, all tests continue to pass:\r\n\r\n```diff\r\ndiff --git a/Lib/typing.py b/Lib/typing.py\r\nindex 1dd9398344..98e19644a2 100644\r\n--- a/Lib/typing.py\r\n+++ b/Lib/typing.py\r\n@@ -1931,6 +1931,7 @@ def _proto_hook(other):\r\n                     if (isinstance(annotations, collections.abc.Mapping) and\r\n                             attr in annotations and\r\n                             issubclass(other, Generic) and getattr(other, '_is_protocol', False)):\r\n+                        1/0\r\n                         break\r\n```\r\n\r\nThe `break` on line 1934 here is unreachable; thus, this whole block of code is pointless:\r\n\r\nhttps://github.com/python/cpython/blob/3af2dc7588614c65e9d1178ad9b4a11a19c14dde/Lib/typing.py#L1929-L1934\r\n\r\nI think we can say for sure that the `break` here is unreachable. This is the `__subclasshook__` method that is monkey-patched onto all subclasses of `typing.Protocol` that do not define their own `__subclasshook__` methods. This block of code in the `__subclasshook__` method is inspecting the `__annotations__` dictionary of `other` to see if it can find any protocol members in that dictionary. _But_ we know that there can't be any protocol members in the `__annotations__` dictionary, because if there were, that would make `other` a protocol with at least one non-callable member. If it's a protocol that has at least one non-callable member, the `__subclasshook__` method is never called at all during `isinstance()` or `issubclass()` checks, because we raise `TypeError` in `_ProtocolMeta.__subclasscheck__`, short-circuiting the call to `abc.ABCMeta.__subclasscheck__` that would call `Protocol.__subclasshook__`:\r\n\r\nhttps://github.com/python/cpython/blob/3af2dc7588614c65e9d1178ad9b4a11a19c14dde/Lib/typing.py#L1828-L1831\r\n\r\nI believe that this block of code can therefore be safely deleted.\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-105835\n* gh-105859\n* gh-105860\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/AlexWaygood","@type":"Person","name":"AlexWaygood"},"datePublished":"2023-06-15T18:22:48.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/105834/cpython/issues/105834"}