Exposing a pointer in Boost.Python

Question

I have this very simple C++ class:

class Tree {
    public:
        Node *head;
};
BOOST_PYTHON_MODULE(myModule)
{

   class_<Tree>("Tree")
        .def_readwrite("head",&Tree::head)
    ;

}

I want to access the head variable from Python, but the message I see is:

No to_python (by-value) converter found for C++ type: Node*

From what I understand, this happens because Python is freaking out because it has no concept of pointers. How can I access the head variable from Python?

I understand I should use encapsulation, but I'm currently stuck with needing a non-encapsulation solution.

Vlad the Impala · Accepted Answer · 2010-03-29 21:55:41Z

21

Of course, I find the answer ten minutes after asking the question...here's how it's done:

class_<Tree>("Tree")
    .add_property("head",
     make_getter(&Tree::head, return_value_policy<reference_existing_object>()),
     make_setter(&Tree::head, return_value_policy<reference_existing_object>()))
;

answered Mar 29, 2010 at 21:55

Vlad the Impala

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1 Comment

elmo Over a year ago

That doesn't sound correct. Most probably you want return_internal_reference.

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