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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"warnings.deprecated leads to incorrectly set _is_protocol on subclasses","articleBody":"# Bug report\n\n### Bug description:\n\n```python\nfrom warnings import deprecated\nfrom typing import Protocol\n\n\nclass FooProtocol(Protocol):\n    pass\n\nclass Base:\n    pass\n\n@deprecated(\"\")\nclass DeprecatedBase:\n    pass\n\nclass FooWithBase(Base, FooProtocol):\n    pass\n\nclass FooWithDeprecatedBase(DeprecatedBase, FooProtocol):\n    pass\n\n\nassert FooWithBase._is_protocol is False\nassert FooWithDeprecatedBase._is_protocol is True\n```\n\n\n### CPython versions tested on:\n\n3.13\n\n### Operating systems tested on:\n\nmacOS\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-138210\n* gh-138561\n* gh-138564\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/hmwillson","@type":"Person","name":"hmwillson"},"datePublished":"2025-08-20T22:13:20.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/138010/cpython/issues/138010"}