Support PyLong_AsNativeBytes()?

[skirpichev]

I would guess it wasn't supported, well, for obvious reasons (complexity).

But if it's going to be used in PyLong_Export() - maybe we should revisit it?

[vstinner]

The implementation is about 186 lines. IMO it's too big and too complex for pythoncapi-compat sadly :-( The https://github.com/vstinner/deadparrot would be a better place to backport such feature.

[skirpichev]

Then maybe using PyLong_AsLongAndOverflow() is better for PyLong_Export. I did pr to switch: vstinner/cpython#6. This clear practical need for backport.

[vstinner]

You shouldn't worry about pythoncapi-compat: there is a great freedom on how we can do things in pythoncapi-compat. It shouldn't impact PEP 757 design.

[skirpichev]

Sure, we could use PyLong_AsLongAndOverflow() just for backports. But it looks faster than current solution, at least for my benchmarks.