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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Errors during `array` module import result in double-DECREF","articleBody":"# Crash report\n\n### What happened?\n\nIn DEBUG build:\n```python\nimport collections.abc\n\ndel collections.abc.MutableSequence\nimport array\n```\nor:\n```\nsys.setrecursionlimit(25)\nimport array\n```\n\ngenerates a double DECREF on the array `ArrayType` object due to poisoned module state:\n\n```text\nPython/gc.c:96: gc_decref: Assertion \"gc_get_refs(g) \u003e 0\" failed: refcount is too small\nobject type name: type\nobject repr     : \u003cclass 'array.array'\u003e\nFatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed\n```\n\n### Analysis\n\nSo, `array_modexec` creates the `ArrayType` and assigns it to array state:\nhttps://github.com/python/cpython/blob/836b2069c86e25cf9456e9210bb612e5166d0779/Modules/arraymodule.c#L3400\n\n It then goes on to do some other setup tasks, and if any of these fail, it DECREF's `state-\u003eArrayType` but leaves the type object on the state struct:\n\nhttps://github.com/python/cpython/blob/836b2069c86e25cf9456e9210bb612e5166d0779/Modules/arraymodule.c#L3409-L3421\n\nReturning `-1` error code.\n\n`PyModule_ExecDef` passes the -1 up the chain:\nhttps://github.com/python/cpython/blob/0514489372f24e8ada518c82ab246de6a22aa3f7/Objects/moduleobject.c#L793\nwhich ends up with an exception in _bootstrap.py:\nhttps://github.com/python/cpython/blob/0514489372f24e8ada518c82ab246de6a22aa3f7/Lib/importlib/_bootstrap.py#L910-L915\n\nAt this point, the array module refcount falls and it's cleaned up, and `array_clear` calls:\nhttps://github.com/python/cpython/blob/2d7a74ece7884c9a5f52cc6ac38a6e7ee691b26c/Modules/arraymodule.c#L3346\nbecause the `ArrayType` pointer is still in the module `state`, this generates the double DECREF\n\n\n\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nLinux\n\n### Output from running 'python -VV' on the command line:\n\nPython 3.16.0a0 (heads/main-dirty:1034e73, Jul  6 2026, 11:11:46) [Clang 22.1.6 ]\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-153238\n* gh-153239\n* gh-153249\n* gh-153250\n* gh-153251\n* gh-153261\n* gh-153274\n* gh-153275\n* gh-153289\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/stestagg","@type":"Person","name":"stestagg"},"datePublished":"2026-07-06T14:57:31.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/153210/cpython/issues/153210"}