[C++-sig] Problem with PyMethodDef and non-static functions

[Jon Kristensen]

tor 2006-09-28 klockan 14:50 -0400 skrev Stefan Seefeld:
> Jon Kristensen wrote:
> > Hello list!
> > 
> > I'm using Python/C to be able to have simple Python scripts in my
> > application. I was free of problems until I switched from using static
> > and global functions to using non-static class methods:
> > 
> > python.cpp:101: error: argument of type ‘PyObject* (Python::)(PyObject*,
> > PyObject*)’ does not match ‘PyObject* (*)(PyObject*, PyObject*)’
> > 
> > After some time I understood that this was a problem that a little
> > tweaking around wouldn't solve. So I want to ask you guys if you can
> > describe how to get around this. I wouldn't want to add any additional
> > dependencies such as SWIG or Boost. Please also note that I'm not that
> > experienced with Python.
> 
> As you have found out, ordinary pointers and pointers to members are
> fundamentally incompatible with each other, i.e. there is no way to
> cast from one to the other.
> You have to implement a wrapper around your method call. Something like:
> 
> struct MyType
> {
>   int func(int);
> };
> 
> PyObject *my_method(PyObject *self, PyObject *args)
> {
>   CxxType *object = extract_object_from_self(self);
>   int arg = extract_arg(args);
>   int result = object->func(arg);
>   return convert_result_to_python(result);
> }

Thanks for your reply. I don't understand the following:

      * What purpose does the struct MyType serve?
      * What's extract_object_from_self? (Don't find anything on
        Google.)

> But of course, all this forward and backward extraction / conversion
> business makes the above highly inconvenient and non-scalable, so you may
> indeed want to give boost.python a try as your project grows. :-)

OK, perhaps I will! :-)

> HTH,
> 		Stefan
> 
-- 
Jon Kristensen