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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"3.13.2: cast in Py_XDECREF causes runtime failures with immortal objects","articleBody":"# Bug report\n\n### Bug description:\n\nIn Python 3.13.2 I use\n```python\nPy_XDECREF(PyObject *op) \n```\nIt is called at the end of a function-call to load an image (cv2.imread) which fails, resulting in a None value (not NULL!). For Python 3.9 Py_XDECREF works just fine, without crash. For Python 3.13.2 the program, compiled with VS2022 (64 Bit), raises a \"Run-Time Check Failure #1 - A cast to a smaller data type has caused a loss of data.\" and my application crashes (\"/RTC1 = Basic Runtime Checks enabled\").\n\nI followed up the calls:\n```python\n    Py_DECREF\n        _Py_IsImmortal\n            #elif SIZEOF_VOID_P \u003e 4\n                _Py_CAST(PY_INT32_T, op-\u003eob_refcnt)     \u003c-- crash\n```\n\nThe value is\n```python\nop-\u003eob_refcnt == 0x0000000100000000\n```\n\nTo fix this problem, I propose, that the type cast to 32 bit should be changed to \n```python\n_Py_CAST(PY_INT32_T, op-\u003eob_refcnt \u0026 0xFFFFFFFF)\n```\n\n### CPython versions tested on:\n\n3.13\n\n### Operating systems tested on:\n\nWindows","author":{"url":"https://github.com/Jejos","@type":"Person","name":"Jejos"},"datePublished":"2025-06-20T09:39:43.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":17},"url":"https://github.com/135746/cpython/issues/135746"}