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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"3.14 regression: slot dataclasses classes leak original class","articleBody":"# Bug report\n\n### Bug description:\n\nWhile trying to test cattrs on 3.14 I ran into this issue. Here's a simple reproducer that passes on 3.13, but doesn't on 3.14.\n\n```python\nimport gc\nfrom dataclasses import dataclass\n\n\n@dataclass(slots=True)\nclass B:\n    b: int\n\n\ngc.collect()\n\nassert [\n    o for o in gc.get_objects() if hasattr(o, \"__name__\") and o.__name__ == \"B\"\n] == [B]\n```\n\nOriginally I ran into this issue with slotted _attrs_ classes but the core problem is the same. Since slotness cannot be added to a class, dataclasses and attrs classes create a class copy with slots instead. The old class used to hang around until a GC collection happened (guess there are some reference cycles, but I never investigated thoroughly).\n\nOn 3.14, a full GC collection does not clean up the original class, causing a leak. Apart from leaking, in case of subclassing the original class will remain in the list of the parent `.__subclasses__()`, causing an issue.\n\n### CPython versions tested on:\n\n3.14\n\n### Operating systems tested on:\n\nmacOS\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-135230\n* gh-136893\n* gh-136960\n* gh-136966\n* gh-137013\n* gh-137014\n* gh-137047\n* gh-137666\n* gh-144021\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/Tinche","@type":"Person","name":"Tinche"},"datePublished":"2025-06-06T23:15:44.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":30},"url":"https://github.com/135228/cpython/issues/135228"}