call C++ using Eigen Library function in python

I'm doing some calculations in C++ with help of Eigen Library, the function is like this:

MatrixXd Cov(MatrixXd Data)
{

  VectorXd meanVector;
  ...
  return Covariance;
}

..in the wrap python function:

static PyObject *Wrap_Cov(PyObject *self,PyObject *args)
{   
      Pyobject *Objectdata;

      if(!PyArg_ParseTuple(args,"O", &ObjectData))
        return NULL;

      Cov(ObjectData);

      return Py_BuildValue("O",&covariance_answer);

  }

Obviously, Python doesn't know the ''object'' I defined, it can't translate ''MatrixXd'' to ''Object'', I think it's some kinds of ''array'', not ''object''

How can I do this without using boost?