How to convert a python object from a C++ library to JSON?

Question

I created a shared library using boost.python and py++. I can instantiate objects from types defined in the library. I want to encode/decode these objects via json. I use jsonpickle module. But, it doesn't encode attributes. I did some research. Most probably the problem occurs because encoded object's __dict__ is empty.

Sample class in the shared library:

struct Coordinate
{
    int x;
    int y;
    Coordinate(int aX, int aY);
}; 

This is python wrapper:

BOOST_PYTHON_MODULE(pyplusplus_test){
    bp::class_< Coordinate >( "Coordinate", bp::init< int, int >(( bp::arg("aX"), bp::arg("aY") )) )
        .enable_pickling()
        .def_readwrite( "x", &Coordinate::x )
        .def_readwrite( "y", &Coordinate::y );
  //...
}

Code piece from python:

cord = pyplusplus_test.Coordinate(10,10)
cord.x = 23
cord.y = -11
tmpStr = jsonpickle.encode(cord)
print tmpStr

And, the output:

{"py/object": "pyplusplus_test.Coordinate"}

Notice that there is no x or y in json output.

Any suggestion?

Thanks.