C API: Consider adding public PyLong_AsByteArray() and PyLong_FromByteArray() functions · Issue #111140 · python/cpython (original) (raw)

Feature or enhancement

The private _PyLong_AsByteArray() and _PyLong_FromByteArray() functions were removed in Python 3.13: see PR #108429.

@scoder asked what is the intended replacement for _PyLong_FromByteArray().

The replacement for _PyLong_FromByteArray() is PyObject_CallMethod((PyObject*)&PyList_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).

The 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).

I propose to add public PyLong_AsByteArray() and PyLong_FromByteArray() functions to the C API.

Python 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:

• PyUnstable_Long_IsCompact()
• PyUnstable_Long_CompactValue()

So having a reliable and simple way to import/export a Python int object as bytes became even more important.

A code search for _PyLong_AsByteArray in PyPI top 5,000 projects found 12 projects using it:

• Cython (0.29.36)
• blspy (2.0.2)
• catboost (1.2)
• fastobo (0.12.2)
• gevent (22.10.2)
• guppy3 (3.1.3)
• line_profiler (4.0.3)
• msgspec (0.16.0)
• orjson (3.9.1)
• pickle5 (0.0.12)
• pyodbc (4.0.39)
• rlp (3.0.0)

Linked PRs

• gh-111140: Adds PyLong_AsNativeBytes and PyLong_FromNative[Unsigned]Bytes functions #114886
• gh-111140: Minor doc fixes for PyLong_AsNativeBytes #115375
• gh-111140: Improve PyLong_AsNativeBytes API doc example & improve the test #115380
• gh-111140: Fix edge case in PyLong_AsNativeBytes where large negative longs may require an extra byte #116053
• gh-111140: minor docs typos cleanup in the C example API calls. #118612