Inherit classes from external compiled modules

[fbxiang]

I am trying to create an extension library that creates subclasses of an existing class in an external library. I will use pytorch as a simplified example to demonstrate it.

Here I would like to inherit the torch Tensor class and create the MyTensor class. Later, I can pass MyTensor objects to external functions that takes a at::Tensor as an input.

#include <ATen/ATen.h>
#include <torch/extension.h>
#include <pybind11/pybind11.h>
#include <pybind11/stl.h>

class MyTensor : public at::Tensor {};

namespace py = pybind11;
PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
  auto Base = py::module_::import("torch").attr("Tensor");
  py::class_<MyTensor>(m, "MyTensor", Base);
}

This code crashes on import at this line with a nullptr passed to get_type_info. I am trying to follow the doc here, and PYBIND11_EXPORT does not seem to help.

Also a (possibly) related question, what is the preferred to way to use classes in an external library as parameters/return values in my extension library? pytorch appears to achieve this but I do not see exactly how it is done.