From comp.python.c++ newsgroup:

1. The constructors of some classes I am trying to wrap are private because instances must be created by using a factory. Is it possible to wrap such classes using bpl v2?

Sure. Of course you can only create the instances using the factory...

If you look at libs/python/test/test_pointer_adoption.cpp you'll see the factory function "create" is being used to generate new instances of class A. It uses return_value_policy<manage_new_object> to instruct Python to adopt the A* to hold the instance.

A* create(std::string const& s)
{
    return new A(s);
}

BOOST_PYTHON_MODULE_INIT(test_pointer_adoption_ext)
{
        def("num_a_instances", num_a_instances);

        // Specify the manage_new_object return policy to take
        // ownership of create's result
        def("create", create, return_value_policy<manage_new_object>());
        
        class_<A>()
            .def("content", &A::content)
            .def("get_inner", &A::get_inner, return_internal_reference<>())
        ;
}

2.