pybind11 custom type segmentation fault

Question

I try to write python bindings with pybind11. Since I also need non simple python types I have to create custom type casters. My problem is that whenever I call get_point from python the LPoint2d will be returned but the following command will lead to a segmentation fault.

As far as I understand the python reference counting may cause that error. But since I am quite new to pybind11 I am not sure. How do I avoid that error?

In the following example I used an LPoint2d from panda3d as an example type. But the error also occurs with other types (e.g. cv2.KeyPoint).

Python:

>>> from panda3d.core import LPoint2d
>>> import test_module as tm
>>> foo = tm.Test()
>>> foo.get_point()
LPoint2d(0, 0)
>>> bar = 42
Segmentation fault (core dumped)

c++ code:

#include <pybind11/pybind11.h>

#include <panda3d/lpoint2.h>

class Test
{
public:
    Test(){}

    LPoint2d getPoint(){
        return m_point;
    }

    void setPoint(LPoint2d &p){
        m_point = p;
    }

private:
    LPoint2d m_point;
};

namespace py = pybind11;

namespace pybind11 { namespace detail {

template <> struct type_caster<LPoint2d> {
    public:

    PYBIND11_TYPE_CASTER(LPoint2d, _("LPoint2d"));

        bool load(handle src, bool) {
            value = LPoint2d(4,2);
            return true;
        }

        static handle cast(const LPoint2d &lp, return_value_policy, handle defval) {
            py::object p3d = py::module::import("panda3d.core");
            py::object plp = p3d.attr("LPoint2d")(lp.get_x(), lp.get_y());

            return {plp.ptr()};
        }
};

}}

PYBIND11_MODULE(test_module, m) {

  py::class_<Test>(m, "Test")
    .def(py::init<>())
    .def("get_point", &Test::getPoint)
    .def("set_point", &Test::setPoint)
    ;

}

Answer 1

It seems that just increasing the reference counter solves this issue.

static handle cast(const LPoint2d &src, return_value_policy policy, handle parent) {
        py::object p3d = py::module::import("panda3d.core");
        py::object plp = p3d.attr("LPoint2d")(src.get_x(), src.get_y());
        plp.inc_ref();

        return plp.ptr();
    }

This is probably not a good solution but it seems to work for now.