How to send a PyCapsule from C++ to python using pybind11

Question

I am trying to pass a PyCapsule from C++ to python using pybind11, but cant seem to figure out how to do it. Ive spent a couple of days reading the docs, but cant get my head round how to make this work.

I have created a class that i would like to send to python. I have tried to create an instance of py::capsule in C++ in function getDataTensor and pass that to python using PYBIND11_MODULE. When try the code below, i get the following error msg:

TypeError: Unable to convert function return value to a Python type! The signature was
    () -> DLTensor

Any guidance on how to solve this problem would be greatly appreciated.

My code is below:

class DLTensor{
public:
    double* data;
    int size;

    DLTensor():data{new double[10]},size{10}{}
};

py::capsule getDataTensor() { 
    std::unique_ptr<DLTensor> dlptr =std::unique_ptr<DLTensor>(new DLTensor());
    auto pybind_capsule= py::capsule(&dlptr,"DLTensorData",nullptr);
    return pybind_capsule; 
    }


namespace py = pybind11;

PYBIND11_MODULE(DBDLTensor, m) {
    m.def("getDataTesor", getDataTensor);

}

Answer 1

I managed to get the code working, so i decided to post my method.
I was missing a py:class_ definition in the PYBIND11_MODULE, and i was missing an ampersand when returning the result to python.

see the working code below:

class DLTensor{
public:
    double* data;
    int size;

    DLTensor():data{new double[10]},size{10}{
    }
};

py::capsule getCapsuleDataTensor() { 
    DLTensor dltensor;
    auto pybind_capsule= py::capsule(&dltensor,"dltensor",nullptr);
    return pybind_capsule; 
    }

namespace py = pybind11;

PYBIND11_MODULE(DBDLTensor, m) {
    py::class_<DLTensor>(m, "DLTensor");
    m.def("getCapsuleDataTensor", &getCapsuleDataTensor);
}