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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`SyntaxError.__init__` memory leak on re-initialization","articleBody":"# Bug report\n\n### Bug description:\n\nThis is a sub-issue for #146102 and more information can be found [here`](https://gist.github.com/devdanzin/1c1e9ba549c26332c387b23406c84ad5).\n\n---\n\nWhen re-initializing a `SyntaxError` (by calling its `__init__` method), it currently does not decref its prior values. This reproducer crashes with ASan:\n```python \ne = SyntaxError(\"msg\", (\"file.py\", 1, 2, \"txt\", 2, 3))\ne.__init__(\"new_msg\", (\"new_file.py\", 2, 3, \"new_txt\", 3, 4))\n\n```\n\n\u003cdetails\u003e\u003csummary\u003eASan report\u003c/summary\u003e\n\u003cp\u003e\n\n```shell\n\n=================================================================\n==576215==ERROR: LeakSanitizer: detected memory leaks\n\nDirect leak of 72 byte(s) in 1 object(s) allocated from:\n    #0 0x7fb60c520cb5 in malloc (/usr/lib/libasan.so.8+0x120cb5) (BuildId: 0b96d08695bbce2da9d4770c29ad2e72fb536f47)\n    #1 0x5600a9805972 in _PyMem_RawMalloc Objects/obmalloc.c:65\n    #2 0x5600a9804d63 in _PyMem_DebugRawAlloc Objects/obmalloc.c:3043\n    #3 0x5600a9804dc7 in _PyMem_DebugRawMalloc Objects/obmalloc.c:3076\n    #4 0x5600a9806748 in _PyMem_DebugMalloc Objects/obmalloc.c:3241\n    #5 0x5600a982ecf3 in PyObject_Malloc Objects/obmalloc.c:1649\n    #6 0x5600a98cdf45 in PyUnicode_New Objects/unicodeobject.c:1318\n    #7 0x5600a98d3471 in unicode_decode_utf8 Objects/unicodeobject.c:5273\n    #8 0x5600a98df566 in PyUnicode_DecodeUTF8Stateful Objects/unicodeobject.c:5381\n    #9 0x5600a96eeb3b in _PyPegen_decode_string Parser/string_parser.c:245\n    #10 0x5600a96ef0b0 in _PyPegen_parse_string Parser/string_parser.c:338\n    #11 0x5600a95ce09e in _PyPegen_constant_from_string Parser/action_helpers.c:1480\n    #12 0x5600a95e9b7a in string_rule Parser/parser.c:17349\n    #13 0x5600a963ed92 in _tmp_156_rule Parser/parser.c:37961\n    #14 0x5600a963f435 in _loop1_82_rule Parser/parser.c:33521\n    #15 0x5600a96486ab in strings_rule Parser/parser.c:17420\n    #16 0x5600a9605530 in atom_rule Parser/parser.c:15361\n    #17 0x5600a9607dce in primary_raw Parser/parser.c:14999\n    #18 0x5600a96083ed in primary_rule Parser/parser.c:14797\n    #19 0x5600a9608da2 in await_primary_rule Parser/parser.c:14751\n    #20 0x5600a960934c in power_rule Parser/parser.c:14627\n    #21 0x5600a960af00 in factor_rule Parser/parser.c:14577\n    #22 0x5600a960d6b4 in term_raw Parser/parser.c:14418\n    #23 0x5600a960dcd3 in term_rule Parser/parser.c:14161\n    #24 0x5600a960e9e5 in sum_raw Parser/parser.c:14114\n    #25 0x5600a960f037 in sum_rule Parser/parser.c:13993\n    #26 0x5600a9610687 in shift_expr_raw Parser/parser.c:13953\n    #27 0x5600a9610cd9 in shift_expr_rule Parser/parser.c:13813\n    #28 0x5600a9611502 in bitwise_and_raw Parser/parser.c:13773\n    #29 0x5600a9611b54 in bitwise_and_rule Parser/parser.c:13691\n\nSUMMARY: AddressSanitizer: 72 byte(s) leaked in 1 allocation(s).\n\n``` \n\n\u003c/p\u003e\n\u003c/details\u003e \n\nThe fix is to call `Py_XDECREF` before replacing the entries in the `SyntaxError` object.\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-146251\n* gh-146517\n* gh-146519\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/brijkapadia","@type":"Person","name":"brijkapadia"},"datePublished":"2026-03-21T11:42:21.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/146250/cpython/issues/146250"}