[pygtk] TypeError: multiple bases have instance lay-out conflict

[Josh Green]

I'm a developer for a GObject/GTK based project called Swami which makes
use of PyGTK to create its Python bindings.  I'm experiencing a crash
with Swami when using PyGTK 2.8.6 which does not occur when using PyGTK
2.8.2.  I hope someone here can help me fix this problem.  I suspect a
PyGTK bug for the crash, but as to what is triggering it I'm not sure.

The crash occurs when the following Python code is executed from within
the C code of the GUI:

PyRun_SimpleString ("swamigui.root = swamigui.swamigui_get_root()\n")

This causes:
TypeError: multiple bases have instance lay-out conflict
Segmentation fault (core dumped)

'swamigui' is the Python module name for the Swami GUI.  The
swamigui_get_root() function is written as an override method, and its
contents are this:

override swamigui_get_root kwargs
static PyObject *
_wrap_swamigui_get_root (PyObject *self, PyObject *args,
                         PyObject *kwargs)
{
    /* pygobject_new handles NULL checking */
    return pygobject_new((GObject *)swamigui_root);
}


swamigui_root is a global pointer to an object of type SwamiguiRoot
(inheritance: GObject->SwamiLock->SwamiRoot->SwamiguiRoot).

The "TypeError: multiple ..." is printed from gobject/pygobject.c:624
(PyGtk 2.8.6) from this code in pygobject_new_with_interfaces():

type = (PyTypeObject*)PyObject_CallFunction((PyObject*)&PyType_Type, "sNN", type_name, bases, dict);

g_free(type_name);

if (type == NULL) {
  PyErr_Print();                  <----  Here the "TypeError: .."
  pyg_gil_state_release(state);
  return NULL;
}


The crash occurs at pygobject.c:725:

722             PyTypeObject *tp = pygobject_lookup_class(G_OBJECT_TYPE(obj));
723             /* need to bump type refcount if created with
724                pygobject_new_with_interfaces(). fixes bug #141042 */
725             if (tp->tp_flags & Py_TPFLAGS_HEAPTYPE)
726                 Py_INCREF(tp);

NULL is returned from pygobject_lookup_class() in response to the
TypeError, and then tp is accessed (although it is NULL).


I think the crash is a PyGTK bug (return of pygobject_lookup_class()
should be checked), but I'm not sure why the TypeError is occurring
(which is triggering this bug).  I fixed a problem with identical output
and resulting crash previously, which was related to a type not being
bound properly as a PyGTK GObject.  I've checked the python binding defs
files for the SwamiguiRoot type though and all seems in order.  Running
this same bit of Python code in a python interpreter works fine, its
only when it is executed from within the C code (although I may be
overlooking something else).  Any help would be greatly appreciated.
Best regards,
	Josh Green