Boost python, class bindings in multiple statements

#include <boost/python.hpp>

namespace bp = boost::python;

struct test
{
    void one() {}
    void two() {}
    void three() {}
};

int main()
{
    Py_Initialize();

    bp::object main_module = bp::import("__main__");
    bp::object main_namespace = main_module.attr("__dict__");

    {
        bp::class_<test> test_binding = bp::class_<test>("test");
        test_binding.def("one", &test::one);
        test_binding.def("two", &test::two);
        test_binding.def("three", &test::three);

        main_namespace["test"] = test_binding;
    }

    try {
        exec("print dir(test)\n", main_namespace);
    } catch (bp::error_already_set &) {
        PyErr_Print();
    }

    return 0;
}