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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Python3.10.5 Pattern Matching Excessive Memory Consumption","articleBody":"\u003c!--\r\n  Use this template for hard crashes of the interpreter, segmentation faults, failed C-level assertions, and similar.\r\n  Do not submit this form if you encounter an exception being unexpectedly raised from a Python function.\r\n  Most of the time, these should be filed as bugs, rather than crashes.\r\n\r\n  The CPython interpreter is itself written in a different programming language, C.\r\n  For CPython, a \"crash\" is when Python itself fails, leading to a traceback in the C stack.\r\n--\u003e\r\n\r\n**Crash report**\r\n\r\n\r\nWhile writing some code to match a particularly complicated AST, I accidentally wrote a function whose definition causes the Python 3.10.5 interpreter to rapidly consume memory. On my system, it consumed approximately 24 GBs of memory before being killed.\r\n\r\nThe function is as follows:\r\n\r\n```python\r\ndef defines(self):\r\n        match self.ast:\r\n                case [S('CoqAst'), [[S('v'), [_, _, [S('expr'), [S('VernacDefinition'), [S('NoDischarge'), S('Definition')], [[[S('v'), [S('Name'), [S('Id'), S(name)]]], _], []], [S('DefineBody'), [], [], [_, _], []]]]]], _]]\r\n                | [S('CoqAst'), [[S('v'), [[S('control'), []], [S('attrs'), []], [S('expr'), [S('VernacStartTheoremProof'), S('Theorem'), [[[[[S('v'), [S('Id'), name]], _], []], _]]]]]], _]]:\r\n                        return name\r\n\r\n```\r\n\r\nTo replicate, paste the above function into a python file and run it.\r\n\r\n**Error messages**\r\n\r\n\r\nOOM killing produced no output, save for `Killed`. \r\n\r\n\r\n**Your environment**\r\n\r\n\u003c!-- Include as many relevant details as possible about the environment you experienced the bug in --\u003e\r\n\r\n- CPython versions tested on: 3.10.5\r\n- Operating system and architecture: Tested on both Windows 10 and ArchLinux. \r\n\r\n\u003c!--\r\nYou can freely edit this text. Remove any lines you believe are unnecessary.\r\n--\u003e\r\n","author":{"url":"https://github.com/tom-p-reichel","@type":"Person","name":"tom-p-reichel"},"datePublished":"2022-06-10T08:07:00.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/93671/cpython/issues/93671"}