/* Multiply = my_def.Multiply */
PyObject *multiply = PyObject_GetAttrString(myDef, "Multiply");
if(multiply && PyCallable_Check(multiply)) {
  /* res = Multiply(4, 5) */
  PyObject *res = PyObject_CallFunction(multiply, "ii", 4, 5);
  if(res) {
    /* print res */
    printf("%d\n", (int)PyInt_AsLong(res));
    Py_XDECREF(res);
  }
  Py_XDECREF(multiply);
}