Add portable way to extract all digits of a `PyLongObject` from C?

[pitrou (Antoine Pitrou)]

@markshannon

I’m in favour of adding a C API. If we say “call int.to_bytes using PyObject_CallMethod()”, then C developers will decide that is too slow and access the internal data structure, whether we like it or not.

Definitely. There are many situations where you don’t want to pay the price of a Python method call just to access the value of a long integer.

[steve.dower]

@markshannon

We are moving to 30 bit digits internally, although 15 bits are still supported, so an API that copied to and from a 30 bit digit array would make sense.

I’d rather not expose this implementation detail. If we add a C API, it should probably just call into the existing implementation to convert into 8-bit digits, or at most, 64-bit digits. Especially since the request is for a portable API.

Otherwise we’ll one day discover that some other sized digit makes more sense, and then we have to write the conversion into 30 bits. May as well start by reusing the conversion we already have.