Boost::Python issue

#include <boost/python.hpp>
#include <boost/make_shared.hpp>
#include <boost/shared_ptr.hpp>

using namespace boost::python;

class ExampleObject {
public:
    std::string name;

    ExampleObject(const std::string & name) : name(name) {}
    virtual ~ExampleObject() {}
    virtual int some_number() { return 12; }
};

struct ExampleObject_wrapper : ExampleObject, wrapper<ExampleObject> {
    ExampleObject_wrapper(const std::string & name)
        : ExampleObject(name), wrapper<ExampleObject>()
    {}

    virtual int some_number(void) override {
        if( override func_override = this->get_override("some_number"))
            return func_override();
        return default_some_number();
    }

    int default_some_number(void) {
        return this->ExampleObject::some_number();
    }
};

typedef boost::shared_ptr<ExampleObject> ExampleObjectPtr;
typedef boost::shared_ptr<ExampleObject_wrapper> ExampleObject_wrapper_ptr;

ExampleObjectPtr create_example_object(const std::string & name) {
    return boost::make_shared<ExampleObject>(name);
}

void print_name(ExampleObjectPtr object) {
    std::cout << "Example object named '"
        << object->name
        << "', nr = "
        << object->some_number()
        << std::endl;
}

BOOST_PYTHON_MODULE(wraptest) {
    def("create_example_object", &create_example_object);
    def("print_name", &print_name);

    class_<ExampleObject_wrapper, boost::noncopyable, ExampleObject_wrapper_ptr>
        ("ExampleObject", init<const std::string &>())
        .def("some_number", &ExampleObject_wrapper::some_number,
                            &ExampleObject_wrapper::default_some_number)
    ;

}