struct A {
    int i_;

    A(int i)
    : i_(i)
    {}
};

struct B {
    A * a_;

    B(A * a)
    : a_(a)
    {}

    int a_content() 
    {
        return a_ == 0 ? 0 : a_->i_;
    }
};

B * create_B(A * a)
{
    return new B(a);
}    

BOOST_PYTHON_MODULE(test_custodian_and_ward)
{
    class_<A>("A", no_init)
        .def(init<int>())
        // #1
        .def("create_B", &create_B, with_custodian_and_ward_postcall<0,1,
                                    return_value_policy<manage_new_object> >())
        ;

    class_<B>("B1", no_init)
        // #2
        .def(init<A*>()[with_custodian_and_ward_postcall<1,2>()])
        .def("a_content", &B::a_content)
        ;

    class_<B>("B2", no_init)
        // #3
        .def("__init__", make_constructor(&create_B, with_custodian_and_ward_postcall<1,2>()))
        .def("a_content", &B::a_content)
        ;

    class_<B>("B3", no_init)
        // #4
        .def("__init__", make_constructor(&create_B, with_custodian_and_ward_postcall<0,1>()))
        .def("a_content", &B::a_content)
        ;
}

BOOST_PYTHON_MODULE(test_custodian_and_ward)
{
    ...

    class_<B>("B1", no_init)
        .def(init<A*>()[construct_custodian_for<1>()])
        .def("a_content", &B::a_content)
        ;

    class_<B>("B2", no_init)
        .def("__init__", make_constructor(&create_B, construct_custodian_for<1>()))
        .def("a_content", &B::a_content)
        ;
}