[Boost-users] [Boost.Python] Using Inheritance *and* Virtual Functions in a Python Binding

Subject: [Boost-users] [Boost.Python] Using Inheritance *and* Virtual Functions in a Python Binding
From: Dan Bailey (drb_at_[hidden])
Date: 2009-10-20 07:41:11

Hi,

I can't seem to get inheritance and virtual functions to work together 
in a simple python binding:

#include <boost/python.hpp>
using namespace boost::python;

struct Base
{
        virtual ~Base() { }
        void nonVirtualFunc() { }
        virtual void virtualFunc() { }
};

struct Derived : public Base
{
        ~Derived() { }
        void virtualFunc() { }
};

struct BaseWrap: public Base, public wrapper<Base>
{
        void virtualFunc()
        {
                if (override virtualFunc = this->get_override("virtualFunc"))
                        virtualFunc();
                else
                        Base::virtualFunc();
        }
        void default_virtualFunc() { this->Base::virtualFunc(); }
};

BOOST_PYTHON_MODULE(test)
{		
        class_<Base, boost::noncopyable>("__Base")
                .def("nonVirtualFunc", &Base::nonVirtualFunc)
        ;

        class_<BaseWrap, boost::noncopyable>("Base")
                .def("virtualFunc", &Base::virtualFunc, &BaseWrap::default_virtualFunc)
        ;
        
        class_<Derived, bases<Base> >("Derived")
                .def("virtualFunc", &Derived::virtualFunc)
        ;
}

Now in my python interpreter:

 >>> import test
 >>> dir(test.__Base)
[<built-ins>, 'nonVirtualFunc']
 >>> dir(test.Base)
[<built-ins>, 'virtualFunc']
 >>> dir(test.Derived)
[<built-ins>, 'virtualFunc']

Without using BaseWrap to do the virtual functions:

 >>> dir(test.Derived)
[<built-ins>, 'nonVirtualFunc', 'virtualFunc']

It seems that by using the boost python wrapper, I now lose any 
inherited functions, and the nonVirtualFunc does not get defined in the 
subclasses. I may be going about this in the wrong way, but is there a 
way of using inheritance and virtual functions together?

Thanks,
Dan