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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Add Py_SETREF() and Py_XSETREF() macros to the limited C API 3.12","articleBody":"The Py_SETREF() and Py_XSETREF() macros were added to Python 3.6 (and 3.5.2) in 2016 with commit 57a01d3a0ee20ee9eea69b658c6bac0f39541625.\r\n\r\nIn 2017, Serhiy @serhiy-storchaka proposed to add these two macros to the limited C API: https://mail.python.org/archives/list/python-dev@python.org/thread/HGBT2Y4VAZOOU5XI2RPSURDGFBMRJKPO/ But these macros were not added.\r\n\r\nPy_CLEAR() is already part of the limited C API (since Python 3.2) and is very similar to Py_SETREF(). Py_CLEAR() rely on the C preprocessor to get a reference to a variable, so the variable can be set to ``NULL`` without having to pass a pointer to the variable. The usage is ``Py_CLEAR(var)``, rather than ``Py_CLEAR(\u0026var)``. The ``Py_SETREF()`` macro does the same, but the value is passed by the caller, it's not always ``NULL``.\r\n\r\nMultiple projects use these macros. Code search in PyPI top 5000 projects using ``(Py_SETREF|Py_XSETREF)`` regex. 16 projects (177 matching lines in total):\r\n\r\n* bitarray-2.6.0\r\n* coverage-6.4.4\r\n* datatable-1.0.0\r\n* gnureadline-8.1.2\r\n* immutables-0.18\r\n* inflate64-0.3.0\r\n* iteration_utilities-0.11.0\r\n* mypy-0.971\r\n* numpy-1.23.2\r\n* pandas-1.4.4\r\n* pickle5-0.0.12\r\n* python-rapidjson-1.8\r\n* python-snappy-0.6.1\r\n* scipy-1.9.1\r\n* typed_ast-1.5.4\r\n* zstd-1.5.2.5\r\n\r\nnumpy and [the pythoncapi-compat project (code)](https://github.com/python/pythoncapi-compat/blob/75b43a687129f2744d4a2c092458c4caa93e162e/pythoncapi_compat.h#L90-L106) define these macros on Python older than 3.5.2.\r\n\r\nI propose to add Py_SETREF() and Py_XSETREF() macros to the limited C API of Python 3.12.\r\n\r\nBy the way, I recently documented these two macros in Python 3.12 (commit c03e05c2e72f3ea5e797389e7d1042eef85ad37a): https://docs.python.org/dev/c-api/refcounting.html#c.Py_SETREF\r\n\r\nSee also issue #98724 and its PR #99100 which discuss Py_CLEAR(), Py_SETREF() and Py_XSETREF() in length.\r\n\r\n---\r\n\r\nI would prefer exposing *functions* (taking a reference to a variable, ``\u0026var``) which can be used when C macros cannot be used, for example in Rust or other programming languages. But adding *functions* is a different which can be addressed separately.\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-99575\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/vstinner","@type":"Person","name":"vstinner"},"datePublished":"2022-11-18T12:19:12.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/99574/cpython/issues/99574"}