PyObject_SetAttrString - doesn't set instance attribute

[Carl Banks]

On May 1, 4:04 am, Jason <jason.hee... at gmail.com> wrote:
> I'm having a bit of trouble with C/Python bindings. Particularly,
> trying to set an instance variable from C when the object is
> initialised using PyObject_SetAttrString, but nothing seems to happen.
> The C initialisation code is:
>
> static void
> nautilus_python_object_instance_init (NautilusPythonObject *object)
> {
>
>         fprintf(stderr, "nautilus_python_object_instance_init called\n");
>
>         NautilusPythonObjectClass *class;
>         debug_enter();
>
>         class = (NautilusPythonObjectClass*)(((GTypeInstance*)object)-
>
> >g_class);
>
>         object->instance = PyObject_CallObject(class->type, NULL);
>
>         PyObject* test_int = PyInt_FromLong(42);
>
>         if (object->instance == NULL)
>         {
>                 PyErr_Print();
>         }
>         else
>         {
>                 fprintf(stderr, "Setting magic parameter\n");
>                 fprintf(stderr, "From C: ");
>                 PyObject_Print(object->instance, stderr, 0);
>                 fprintf(stderr, "\n");
>                 int retval = PyObject_SetAttrString(object->instance,
> "super_happy_magic", test_int);
>                 fprintf(stderr, "Result: %i\n", retval);
>         }
>
>         Py_DECREF(test_int);
>
> }

Not sure what you're doing here.  It looks like you are being passed
an object of a given type, then you get the type object, call it to
create another object of that type, and assign it to object->instance.


> ...and the Python module contains:
>
> class MenuProviderTest(nautilus.MenuProvider):
>
>     def __init__(self):
>         print "From Python: %s" % self
>
>         try:
>             print getattr(self, "super_happy_magic")
>         except AttributeError:
>             print "Didn't work!"
>
> When the MenuProviderTest is created, the output is:
>
> nautilus_python_object_instance_init called
> Setting magic parameter
> From C: <MenuProvTest.MenuProviderTest object at 0x7faee6a9fcd0>
> Result: 0
> From Python: <MenuProvTest.MenuProviderTest object at 0x7faee6a9fcd0>
> Didn't work!
>
> (I've tried getattr and self.super_happy_magic, with the same effect.)
>
> Where am I going wrong?

You are assigning the attirbute the the object that the C code refers
to as "object->instance", but it seems that in the Python snippet you
are calling getattr on the object that the C code refers to as
"object".


Carl Banks