[C++-sig] inheritance and polyphormism

[Luca Sbardella]

The link doesn't answer the question, or at least I do not see the answer.

At first, I though that using the following approach would work


class derived_wrap: public derived, public boost::python::wrapper<derived>
{
  void method2() {....}
};

class_<derived_wrap, boost::noncopyable, bases<base>>("derived")
        .def("method2",                &derived::method2)
  ;
However in doing so the "method1" of the base class does not behave as
expected.

That is to say, if in Python I do the following

class A(derived):
   def method1(self):
      ......

and I pass A class back to C++, the method1 has not been overwritten!!!
method2 on the other hand works as expected.
Best
Luca


On 09/06/07, Roman Yakovenko <roman.yakovenko at gmail.com> wrote:
>
> On 6/7/07, Luca Sbardella <luca.sbardella at gmail.com> wrote:
> > hi,
> > How do I expose properly a class tree so that classes can be derived
> from
> > python in a polymorphic way?
> > I've approached the problem is the following way.
> >
> > class base  {
> > public:
> >   virtual void method1(){}
> > };
> >
> > class derived: public base  {
> >  public:
> >    virtual void method2(){}
> >  };
> >
> > I then wrote two class templates to wrap the classes in the following
> way
> >
> > template<class T>
> > class base_wrap: public T, public boost::python::wrapper<T>  {
> >   void method1() {....}
> > };
> >
> > template<class T>
> >  class derived_wrap: public base_wrap<T> {
> >    void method2() {....}
> >  };
> >
> > And finally
> >
> > class_<base_wrap<base>, boost::noncopyable>("base")
> >         .def("method1",                &base::method1)
> >   ;
> >
> > class_<derived_wrap<derived>, boost::noncopyable>("derived")
> >         .def("method1",                &derived::method1)     <========
> this
> > seems redundant
> >          .def("method2",                &derived::method2)
> >    ;
> >
> > This works fine, however I does't seem to be the optimal solution (see
> the
> > comment on class_<derived_wrap<derived>>).
> > Is there a better way?
>
> Check this:
>
> http://boost.org/libs/python/doc/tutorial/doc/html/python/exposing.html#python.inheritance
>
> --
> Roman Yakovenko
> C++ Python language binding
> http://www.language-binding.net/
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> C++-sig at python.org
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