def dnd_accept(self, source, event):
    """
    Decide what object will accept the drop.

    The returned object will become the new target for the drop operation.

    :param source: The object being dragged.
    :param event: The tk event that resulted in this call.
                  Usually a motion event.
    :return: The object that will accept a drop - this widget.
    """
    print("dnd_accept. Called on {}. source is {}, event type is {}".format(self, source, event.type))
    return self