Checks to see if the callback pointers are still valid or not.
        
        :return     <bool>

def isValid(self):
        """
        Checks to see if the callback pointers are still valid or not.
        
        :return     <bool>
        """
        if self._callback_func_ref is not None and self._callback_func_ref():
            if self._callback_self_ref is None or self._callback_self_ref():
                return True
        return False