Question

I have two classes, the first called “Radish” and the second called “RadishCont”.
All the code is written in C++ and need to be used in python.

Radish have been exposed to python using SWIG; RadishCont, instead, have been exposed using boost::python.

I need to add a method into the class RadishCont that has this syntax:

Radish* get_radish()
{
    return &radish;
}

Where “radish” is a Radish instance contained in RadishCont.

When I execute the python code I receive this exception:

TypeError: No Python class registered for C++ class Radish

So, my question is: how can I make this method work in python without rewriting RadishCont using SWIG ?

Answer 1

At the end, I have done it.

I have created a class instance in my boost python module like this:

class_<Radish>("Radish");

I have created a converter function like this:

static void* radishConvert(PyObject* obj)
{
    char thisStr[] = "this";
    //first we need to get the this attribute from the Python Object
    if (!PyObject_HasAttrString(obj, thisStr))
            return NULL;

    PyObject* thisAttr = PyObject_GetAttrString(obj, thisStr);
    if (thisAttr == NULL)
            return NULL;
    //This Python Object is a SWIG Wrapper and contains our pointer
    void* pointer = ((PySwigObject*)thisAttr)->ptr;
    Py_DECREF(thisAttr);
    return pointer;
}

Where PySwigObject is a struct like this:

struct PySwigObject 
{
    PyObject_HEAD 
    void * ptr;
    const char * desc;
};

Last, I have registered my converter:

boost::python::converter::registry::insert(&radishConvert, type_id<Radish>());

This perfectly works, I can get objects from SWIG and pass it to boost::python. The inverse process is still unsolved but is enough for me.

This is the guide I have used to find the solution:
http://wiki.python.org/moin/boost.python/HowTo#SWIG_exposed_C.2B-.2B-_object_from_Python