'_PyLong_NumBits': identifier not found in 3.13

Bug report

Bug description:

While fixing pywin32 to let CI builds work in Python 3.13, the build process complained of not being able to find _PyLong_NumBits. All other Python versions in the CI built successfully.

BOOL PyCom_VariantFromPyObject(PyObject *obj, VARIANT *var)
{
    // ...
    if (PyLong_Check(obj)) {
        int sign = _PyLong_Sign(obj);
        size_t nbits = _PyLong_NumBits(obj);
        if (nbits == (size_t)-1 && PyErr_Occurred())
            return FALSE;
    // ...
}

The function still exists in main, apparently inaccessible via the public C API since 3.13. What's the recommended replacement?

CPython versions tested on:

3.8, 3.9, 3.10, 3.11, 3.12, 3.13

Operating systems tested on:

Windows

Linked PRs

In 5846924 Victor restored

_PyLong_Copy()
_PyLong_FromDigits()
_PyLong_New()
_PyLong_Sign()

It seems reasonable to include _PyLong_NumBits as well, since like the others there isn't a great replacement.

Will it be restored in the next beta 3.13 release, or will I have to wait until the first 3.14 alpha release?

pythongh-119336: Restore _PyLong_NumBits

I cannot make that call, but I made #119418 against 3.14 for now (it can be backported for 3.13 if that's what people decide). Eventually it seems like a good idea to make this public.

You can modify pywin32 to call the bit_length() method which returns a Python int object. Then if you need a size_t, you can call PyLong_AsSize_t.

If this function is called by one project, we should consider making it public, rather than restoring the old private function.

You can modify pywin32 to call the bit_length() method which returns a Python int object. Then if you need a size_t, you can call PyLong_AsSize_t.

If this function is called by one project, we should consider making it public, rather than restoring the old private function.

How would I access the built-in bit_length() method within the C API?

How would I access the built-in bit_length() method within the C API?

PyObject_CallMethod(obj, "bit_length", NULL)

(Not taking a view on whether that justifies not restoring the function though)

A code search in PyPI top 7,500 projects found other projects:

mariadb (1.1.10)
pickle5 (0.0.12)
zodbpickle (3.2)

pickle5 and zodbpickle contain copies of the Python source code, but MariaDB is a good usage example. So maybe it's worth it to add a function.

I created issue gh-119714: [C API] Add PyLong_GetNumBits() function.

@encukou

A code search in PyPI top 7,500 projects found other projects:

@encukou also identified that panda3d uses it: https://github.com/panda3d/panda3d/blob/adb92428856853019583f398d27c5d34e44a9343/panda/src/putil/bitArray_ext.cxx#L28

gh-119336: Restore removed _PyLong_NumBits() function (#119418)

Function restored by commit e50fac9

pythongh-119336: Restore removed _PyLong_NumBits() function (pythonGH…

[3.13] gh-119336: Restore removed _PyLong_NumBits() function (GH-119418…

pythongh-119336: Restore removed _PyLong_NumBits() function (python#1…

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'_PyLong_NumBits': identifier not found in 3.13 #119336

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'_PyLong_NumBits': identifier not found in 3.13 #119336

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Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

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emmatyping commented on May 22, 2024

clin1234 commented on May 22, 2024

emmatyping commented on May 22, 2024

vstinner commented on May 28, 2024

clin1234 commented on May 28, 2024

da-woods commented on May 29, 2024

vstinner commented on May 29, 2024

vstinner commented on May 29, 2024

vstinner commented on Jun 3, 2024

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