#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/reference_existing_object.hpp>
#include <boost/python/return_value_policy.hpp>
#include <utility>

// classes to wrap
struct Singleton
{
   Singleton() : x(0) {}
   int exchange(int n)  // set x and return the old value
   {
        std::swap(n, x);
        return n;
   }
   int x;
};

Singleton& get_it()
{
   static Singleton just_one;
   return just_one;
}
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(singleton)
{
    def("get_it", get_it, reference_existing_object());  
    class_<Singleton>("Singleton")
       .def("exchange", &Singleton::exchange)
       ;
}