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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":" C API: Consider adding public PyLong_AsByteArray() and PyLong_FromByteArray() functions","articleBody":"# Feature or enhancement\r\n\r\nThe private `_PyLong_AsByteArray()`  and `_PyLong_FromByteArray()` functions were removed in Python 3.13: see PR #108429.\r\n\r\n@scoder [asked](https://github.com/python/cpython/pull/108429#issuecomment-1772777608) what is the intended replacement for `_PyLong_FromByteArray()`.\r\n\r\nThe replacement for `_PyLong_FromByteArray()` is ``PyObject_CallMethod((PyObject*)\u0026PyList_Type, \"from_bytes\", \"s#s\", str, len, \"big\")`` but I'm not sure what is the easy way to set the *signed* parameter to True (default: `signed=False`).\r\n\r\nThe replacement for `_PyLong_AsByteArray()` is `PyObject_CallMethod(my_int, \"to_bytes\", \"ns\", length, \"big\")`. Same, I'm not sure how to easy set the *signed* parameter to True (default: `signed=False`).\r\n\r\nI propose to add public PyLong_AsByteArray() and PyLong_FromByteArray() functions to the C API.\r\n\r\nPython 3.12 modified PyLongObject: it's no longer a simple array of digits, but it's now a more less straightforward `_PyLongValue` structure which requires using unstable functions to access small \"compact\" values:\r\n\r\n* PyUnstable_Long_IsCompact()\r\n* PyUnstable_Long_CompactValue()\r\n\r\nSo having a reliable and simple way to import/export a Python int object as bytes became even more important.\r\n\r\n---\r\n\r\nA code search for ``_PyLong_AsByteArray `` in PyPI top 5,000 projects found 12 projects using it:\r\n\r\n* Cython (0.29.36)\r\n* blspy (2.0.2)\r\n* catboost (1.2)\r\n* fastobo (0.12.2)\r\n* gevent (22.10.2)\r\n* guppy3 (3.1.3)\r\n* line_profiler (4.0.3)\r\n* msgspec (0.16.0)\r\n* orjson (3.9.1)\r\n* pickle5 (0.0.12)\r\n* pyodbc (4.0.39)\r\n* rlp (3.0.0)\r\n\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-114886\n* gh-115375\n* gh-115380\n* gh-116053\n* gh-118612\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/vstinner","@type":"Person","name":"vstinner"},"datePublished":"2023-10-20T21:39:02.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":61},"url":"https://github.com/111140/cpython/issues/111140"}