[C++-sig] Re: SWIG: overriding virtual functions in Python.

[Jacek Generowicz]

Jacek Generowicz <jacek.generowicz at cern.ch> writes:

> given a C++ class
> 
>   struct foo {
>     virtual void one() {
>       cout << "This is foo::one() calling two()" << endl;
>       two();
>     }
>     virtual void two() {
>       cout << "This is foo::two()" << endl;
>     }
>   };
> 
> I would like to subclass it in Python and override "two()" thus:
> 
>   class bar(foo):
>     def two(self):
>       print "This is bar.two()"
> 
> in such a way that calling bar.one() ...
> 
>   bar().one()
> 
> gives the result
> 
>   This is foo::one() calling two()
>   This is bar.two()
> 
> rather than 
> 
>   This is foo::one() calling two()
>   This is foo.two()
> 
> In Boost this is achieved by doing providing a wrapper class around
> the original C++ implementation, and giving it a default
> implementation of the virtual function, which calls back into Python.
> 
> Is there a way of doing it in SWIG?

Replying to myself for the benefit of anyone searching archives for
a solution to this problem.


The keyword is "directors":

  http://www.swig.org/Doc1.3/Python.html#n32

In brief, for the above example

a) Change 

    %module the_module_name
to 
    %module(directors="1") the_module_name

b) Add

    %feature("director") foo;

anywhere before foo is declared.