Can an object of a C type have random members added? tp_dictoffset?

[Denis S. Otkidach]

On Thu, 21 Apr 2005 17:55:24 +1000 Gregory Bond wrote:

GB> I have a class implemented in C using tp_members to specify (read-only) 
GB> access to data members in the C struct. I'd like to be able to do the 
GB> decoration trick with objects of this class.  Is this possible?
GB> 
GB> [The documentation for tp_dictoffset eseems to hint that this is 
GB> possible..... how do I use it?]

Something like the following:

typedef struct {
        PyObject_HEAD
        PyObject *dict;
} YourObject;

static PyMemberDef module_members[] = {
        {"__dict__", T_OBJECT, offsetof(YourObject, dict), READONLY},
        {0}
};

PyObject *
Your_New()
{
        YourObject *obj;
        obj = PyObject_GC_New(YourObject, &Your_Type);
        if (obj==NUL) return NULL;
        obj->dict = PyDict_New();
        if (obj->dict==NULL) {
                Py_DECREF(obj);
                return NULL;
        }
        PyObject_GC_Track(obj);
        return (PyObject *)obj;
}

PyTypeObject Your_Type = {
        PyObject_HEAD_INIT(&PyType_Type)
        # ...skipped...
        offsetof(YourObject, dict), /* tp_dictoffset */
        # ...skipped...
}

-- 
Denis S. Otkidach
http://www.python.ru/      [ru]