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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Interned strings are immortal, despite what the documentation says","articleBody":"# Bug report\r\n\r\n### Bug description:\r\n\r\nThe [`sys.intern` documentation](https://docs.python.org/3.13/library/sys.html#sys.intern) explicitly says:\r\n\r\n\u003e Interned strings are not [immortal](https://docs.python.org/3.13/glossary.html#term-immortal); you must keep a reference to the return value of [`intern()`](https://docs.python.org/3.13/library/sys.html#sys.intern) around to benefit from it.\r\n\r\nHowever, they were made immortal in https://github.com/python/cpython/pull/19474 (Implement Immortal Objects -- implementation of PEP 683), without a documentation update. The 3.12 What's New also doesn't mention the change. [edit: it's now clear that the PR author (@eduardo-elizondo) intended it but the reviewer (@markshannon) did not]\r\nPEP-683 itself only mentions the change as a possible optimization.\r\n\r\nMeanwhile, `pathlib` [interns every path segment it processes](https://github.com/python/cpython/blob/79970792fd2c70f77c38e08c7b3a9daf6a11bde1/Lib/pathlib/__init__.py#L257), presumably depending on the documented behaviour. In CPython's test suite, that causes names of temporary directories to leak (stealthily, since interned strings are excluded from the total refcount).\r\n[edit: Worse, `type_setattro`, `PyObject_SetAttr` or `PyDict_SetItemString` immortalize keys, so strings used for key/attribute names this way are not reclaimed until interpreter shutdown.]\r\nOn the other hand, free-threading (PEP-703) ~~seems to rely~~ [edit: relies] on these being immortal.\r\n\r\nWhat's the correct behaviour? [edit: specifically, in 3.12 and non-free-threading 3.13, should this change be reverted or documented?]\r\n\r\n@eduardo-elizondo @ericsnowcurrently\r\n\r\n\r\n\u003c!-- gh-linked-prs --\u003e\r\n### Linked PRs\r\n* gh-120520\r\n* gh-120945\r\n* gh-121358\r\n* gh-121364\r\n* gh-121851\r\n* gh-121854\r\n* gh-123065\n* gh-124938\n* gh-127250\n\u003c!-- /gh-linked-prs --\u003e\r\n\r\nRelated fixes:\r\n- https://github.com/python/cpython/pull/121903\r\n- https://github.com/python/cpython/pull/122303\r\n- https://github.com/python/cpython/pull/122421","author":{"url":"https://github.com/encukou","@type":"Person","name":"encukou"},"datePublished":"2024-01-12T16:49:36.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":37},"url":"https://github.com/113993/cpython/issues/113993"}