Runtime Error Uable to cast Python instance to C++ type (complie in debug mode for details)

Errors
1

Test code:

from dolfin import *
import cppimport

compiled_cpp_module = cppimport.imp('delta_interpolation')

mesh = UnitCubeMesh(21, 21, 21)
V = VectorFunctionSpace(mesh, 'CG', 2)

dof_component_map = {}
compiled_cpp_module.extract_dof_component_map_1(dof_component_map, V)

cpp file:

void extract_dof_component_map_1(std::unordered_map<std::size_t,
                               std::size_t>& dof_component_map,
                               const FunctionSpace& V)
{
  std::cout << "hi";
}

PYBIND11_MODULE(delta_interpolation, m)
{
  py::bind_map<std::unordered_map<std::size_t, std::size_t>>(m, "unordered_mapping");

  m.def("extract_dof_component_map_1", (void (*)(std::unordered_map<std::size_t,
                                std::size_t>& , const FunctionSpace&))
      &extract_dof_component_map_1);
  m.def("extract_dof_component_map_1", [](py::dict d, py::object U){
      auto _d = d.cast<std::unordered_map<std::size_t, std::size_t>&>();
      auto _U = U.attr("_cpp_object").cast<const FunctionSpace&>();
      extract_dof_component_map_1(_d, _U);
    });
}

Error:

Line: compiled_cpp_module.extract_dof_component_map_1(dof_component_map, V)
RuntimeError: Uable to cast Python instance to C++ type (complie in debug mode for details)

It should return a “Hi” when running the program. I don’t know the reason that causes the runtime error. When looking at the debug mode, it either didn’t show anything.
I apprieciate any help.