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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Python 3.13 regression: Recursive dataclasses fail to ==: RecursionError: maximum recursion depth exceeded","articleBody":"# Bug report\r\n\r\n### Bug description:\r\n\r\nThere is a regression in comparing recursive dataclasses for equality in Python 3.13.0 from the first alpha until at least a4.\r\n\r\n### Python 3.12\r\n\r\n```pycon\r\n\u003e\u003e\u003e from dataclasses import dataclass\r\n\u003e\u003e\u003e @dataclass\r\n... class C:\r\n...     recursive: object = ...\r\n... \r\n\u003e\u003e\u003e c1 = C()\r\n\u003e\u003e\u003e c1.recursive = c1\r\n\u003e\u003e\u003e c1 == c1\r\nTrue\r\n```\r\n\r\n\r\n### Python 3.13\r\n\r\n```pycon\r\n\u003e\u003e\u003e from dataclasses import dataclass\r\n\u003e\u003e\u003e @dataclass\r\n... class C:\r\n...     recursive: object = ...\r\n... \r\n\u003e\u003e\u003e c1 = C()\r\n\u003e\u003e\u003e c1.recursive = c1\r\n\u003e\u003e\u003e c1 == c1\r\nTraceback (most recent call last):\r\n  File \"\u003cstdin\u003e\", line 1, in \u003cmodule\u003e\r\n    c1 == c1\r\n  File \"\u003cstring\u003e\", line 4, in __eq__\r\n  File \"\u003cstring\u003e\", line 4, in __eq__\r\n  File \"\u003cstring\u003e\", line 4, in __eq__\r\n  [Previous line repeated 996 more times]\r\nRecursionError: maximum recursion depth exceeded\r\n```\r\n\r\nThis has started happening since 18cfc1eea569f0ce72ad403840c0e6cc5f81e1c2.\r\n\r\nPreviously, tuples were compared via `==`, which skips calling `__eq__` for items with the same identity. Now it skips the identity check and compares items directly with `__eq__`, causing `RecursionError`.\r\n\r\nThis breaks sip-build; hence, we cannot build pyqt5 or pyqt6 in Fedora with Python 3.13 to test the entire stack. For details, see this [Fedora bugzilla](https://bugzilla.redhat.com/show_bug.cgi?id=2250649).\r\n\r\n```\r\nsip-build: An internal error occurred...\r\nTraceback (most recent call last):\r\n  File \"/usr/bin/sip-build\", line 8, in \u003cmodule\u003e\r\n    sys.exit(main())\r\n             ^^^^^^\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/tools/build.py\", line 37, in main\r\n    handle_exception(e)\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/exceptions.py\", line 81, in handle_exception\r\n    raise e\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/tools/build.py\", line 34, in main\r\n    project.build()\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/project.py\", line 245, in build\r\n    self.builder.build()\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/builder.py\", line 48, in build\r\n    self._generate_bindings()\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/builder.py\", line 280, in _generate_bindings\r\n    buildable = bindings.generate()\r\n                ^^^^^^^^^^^^^^^^^^^\r\n  File \"/builddir/build/BUILD/PyQt5-5.15.9/project.py\", line 619, in generate\r\n    buildable = super().generate()\r\n                ^^^^^^^^^^^^^^^^^^\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/bindings.py\", line 214, in generate\r\n    output_pyi(spec, project, pyi_path)\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/pyi.py\", line 53, in output_pyi\r\n    _module(pf, spec, module)\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/pyi.py\", line 132, in _module\r\n    _class(pf, spec, module, klass, defined)\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/pyi.py\", line 267, in _class\r\n    _class(pf, spec, module, nested, defined, indent)\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/pyi.py\", line 289, in _class\r\n    _callable(pf, spec, module, member, klass.overloads,\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/pyi.py\", line 485, in _callable\r\n    _overload(pf, spec, module, overload, overloaded, first_overload,\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/pyi.py\", line 575, in _overload\r\n    signature = _python_signature(spec, module, py_signature, defined,\r\n                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/pyi.py\", line 599, in _python_signature\r\n    as_str = _argument(spec, module, arg, defined, arg_nr=arg_nr)\r\n             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/pyi.py\", line 676, in _argument\r\n    s += _type(spec, module, arg, defined, out=out)\r\n         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/pyi.py\", line 710, in _type\r\n    return ArgumentFormatter(spec, arg).as_type_hint(module, out, defined)\r\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/formatters/argument.py\", line 327, in as_type_hint\r\n    s += TypeHintManager(self.spec).as_type_hint(hint, out, context,\r\n         ^^^^^^^^^^^^^^^^^^^^^^^^^^\r\n  File \"/usr/lib64/python3.13/site-packages/sipbuild/generator/outputs/type_hints.py\", line 107, in __new__\r\n    manager = cls._spec_manager_map[spec]\r\n              ~~~~~~~~~~~~~~~~~~~~~^^^^^^\r\n  File \"/usr/lib64/python3.13/weakref.py\", line 415, in __getitem__\r\n    return self.data[ref(key)]\r\n           ~~~~~~~~~^^^^^^^^^^\r\n  File \"\u003cstring\u003e\", line 4, in __eq__\r\n  File \"\u003cstring\u003e\", line 4, in __eq__\r\n  File \"\u003cstring\u003e\", line 4, in __eq__\r\n  [Previous line repeated 495 more times]\r\nRecursionError: maximum recursion depth exceeded in comparison\r\n```\r\n\r\ncc @rhettinger @ericvsmith\r\n\r\nThanks to @swt2c for bisecting the problem. Thanks to @encukou who gave me a hint of what to look for when finding the smaller reproducer.\r\n\r\n### CPython versions tested on:\r\n\r\n3.13\r\n\r\n### Operating systems tested on:\r\n\r\nLinux\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-116790\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/hroncok","@type":"Person","name":"hroncok"},"datePublished":"2024-03-12T10:36:26.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/116647/cpython/issues/116647"}