Binding Python class methods to C++ and run them there

[Dude19735]

Hi, I would like to bind class methods to C++ using nb::callable. For example the method self.test_method:

Class Test:
   def __init__(self):
      pass
   def test_method(self, cpp_func_param):
      cpp_func_param()

On the C++ side, I have the following:

    class Vk_PyFunc : public Vk_Func {
    public:
        Vk_PyFunc(nb::object obj, nb::callable func)
        :
        _func(func),
        _obj(obj),
        Vk_Func(sizeof(Vk_PyFunc) + sizeof(Vk_Func))
        {}

        void operator()(std::function<void()> repeat) override {
			_call_F(repeat);
        }

    private:
        nb::callable _func;
        nb::object _obj;

	auto _call_F(std::function<void()> repeat) -> void
	{
            nb::gil_scoped_acquire acquire;
            try {
                _func(_obj, nb::cpp_function(repeat));
            } catch (const nb::python_error &e) {
                Vk_Logger::Error(typeid(this), "[Python exception]: {0}", e.what());
            }
        }
    };

The important bit is

_func(_obj, nb::cpp_function(repeat));

The issue I'm having is, that it crashes with Nanobind. It used to work with Pybind. I can resolve the issue if I don't put the Python methods inside of a class. But since I need access to the self inside the methods, I ended up tackling the problem by still putting the methods outside of classes, but passing the self-object via an nb::object to C++ and then back as actual argument (this is what the _obj is inside of _func(_obj, nb::cpp_function(repeat));. This works, but is not exactly "nice".

Does anyone know if it is possible to bind class methods to C++ and call them from there using Nanobind, and if so, how? I tried all combinations I could think of.

A full-code Python example is in: https://github.com/Dude19735/Pyke/blob/main/test_py/test_vkviewer.py
The Vk_Func abstraction is in: https://github.com/Dude19735/Pyke/blob/main/src/Vk_Function.hpp
The binding module is: https://github.com/Dude19735/Pyke/blob/main/src/pyexp_vkviewer.cpp (line 675, "vk_register_action")

Thanks a lot for any help with this!

[wjakob]

You can take a look e.g. at how the std::function bindings work, they do something similar. If you need help, then please either make a small reproducer or provide more information (e.g. a backtrace to know what part crashed would be useful).