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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"memory leak in `_PyBytes_FormatEx` error path","articleBody":"# Bug report\n\n### Bug description:\n\n```python\nimport unittest\n\nclass BaseBytesTest:\n    def test_mod(self):\n        def check(fmt, vals, result):\n            bf = self.type2test(fmt)\n            bf = bf % vals\n        check(b'%*b', (2**63-1, b'abc'), b'  abc')\n\nclass ByteArrayTest(BaseBytesTest, unittest.TestCase):\n    type2test = bytearray\n\nif __name__ == \"__main__\":\n    unittest.main()\n```\n\n```\n=================================================================\n==776798==ERROR: LeakSanitizer: detected memory leaks\n\nDirect leak of 60 byte(s) in 1 object(s) allocated from:\n    #0 0x7a4877a6d9c7 in malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:69\n    #1 0x55e03c01bdf1 in _PyMem_RawMalloc ../Objects/obmalloc.c:63\n    #2 0x55e03c01b1c2 in _PyMem_DebugRawAlloc ../Objects/obmalloc.c:2887\n    #3 0x55e03c01b22a in _PyMem_DebugRawMalloc ../Objects/obmalloc.c:2920\n    #4 0x55e03c01caa8 in _PyMem_DebugMalloc ../Objects/obmalloc.c:3085\n    #5 0x55e03c045a95 in PyObject_Malloc ../Objects/obmalloc.c:1493\n    #6 0x55e03bf3d755 in _PyBytes_FromSize ../Objects/bytesobject.c:126\n    #7 0x55e03bf42690 in PyBytes_FromStringAndSize ../Objects/bytesobject.c:156\n    #8 0x55e03bf0bf70 in _PyPegen_parse_string ../Parser/string_parser.c:334\n    #9 0x55e03bdf6370 in _PyPegen_constant_from_string ../Parser/action_helpers.c:1451\n    #10 0x55e03be12662 in string_rule ../Parser/parser.c:17153\n    #11 0x55e03be55755 in _tmp_154_rule ../Parser/parser.c:37189\n    #12 0x55e03be55e08 in _loop1_80_rule ../Parser/parser.c:32749\n    #13 0x55e03be5eede in strings_rule ../Parser/parser.c:17224\n    #14 0x55e03be2f755 in atom_rule ../Parser/parser.c:15165\n    #15 0x55e03be31f78 in primary_raw ../Parser/parser.c:14803\n    #16 0x55e03be325a4 in primary_rule ../Parser/parser.c:14601\n    #17 0x55e03be32f62 in await_primary_rule ../Parser/parser.c:14555\n    #18 0x55e03be3351f in power_rule ../Parser/parser.c:14431\n    #19 0x55e03be350b7 in factor_rule ../Parser/parser.c:14381\n    #20 0x55e03be377b7 in term_raw ../Parser/parser.c:14222\n    #21 0x55e03be37de3 in term_rule ../Parser/parser.c:13965\n    #22 0x55e03be38aa7 in sum_raw ../Parser/parser.c:13918\n    #23 0x55e03be39106 in sum_rule ../Parser/parser.c:13797\n    #24 0x55e03be3a72f in shift_expr_raw ../Parser/parser.c:13757\n    #25 0x55e03be3ad5b in shift_expr_rule ../Parser/parser.c:13617\n    #26 0x55e03be3b55e in bitwise_and_raw ../Parser/parser.c:13577\n    #27 0x55e03be3bbbd in bitwise_and_rule ../Parser/parser.c:13495\n    #28 0x55e03be3c3c0 in bitwise_xor_raw ../Parser/parser.c:13455\n    #29 0x55e03be3ca1f in bitwise_xor_rule ../Parser/parser.c:13373\n\nSUMMARY: AddressSanitizer: 60 byte(s) leaked in 1 allocation(s).\n```\n\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nLinux\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-140957\n* gh-141154\n* gh-141155\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/YuanchengJiang","@type":"Person","name":"YuanchengJiang"},"datePublished":"2025-11-03T08:55:57.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/140939/cpython/issues/140939"}