Methods with two outputs are expected to return an error, methods aren't visible from python

[chibitanaka]

Hi, I'm trying to build this project, https://github.com/holiman/uint256, but I've run into multiple issues:

Suppose we have a function with multiple outputs: func (z *Int) AddOverflow(x, y *Int) (*Int, bool), bind expects second argument to be an error and outputs the following gopy: second result value must be of type error.

To reproduce, minimized testcase:

package uint256

import (
	"math/bits"
)

type Int [4]uint64

func NewInt(val uint64) *Int {
	z := &Int{}
	z.SetUint64(val)
	return z
}

func (z *Int) SetUint64(x uint64) *Int {
	z[3], z[2], z[1], z[0] = 0, 0, 0, x
	return z
}

func (z *Int) AddOverflow(x, y *Int) (*Int, bool) {
	var carry uint64
	z[0], carry = bits.Add64(x[0], y[0], 0)
	z[1], carry = bits.Add64(x[1], y[1], carry)
	z[2], carry = bits.Add64(x[2], y[2], carry)
	z[3], carry = bits.Add64(x[3], y[3], carry)
	return z, carry != 0
}

The second issue I'm having is that after compiling the project, public methods of type Int aren't exposed to Python, e.g. the following code won't run:

from uint256_py import uint256

x, y, z = uint256.NewInt(123), uint256.NewInt(456), uint256.NewInt(0)
z.Add(x, y) # doesn't work, method isn't visible

I suspect this has something to do with Int being represented as an array [4]uint64. Versions I'm using: Go 1.21.3 & Python 3.11.5

It seemed related to #315, so I've run this in docker with Go 1.19.5 & Python3.10.12 but the issue persisted.

Thank you.