def METHOD_NAME(self, event):
    """Returns a tuple reflecting the current selection state
    Parameters
    ----------
    event : enable KeyEvent or MouseEvent
    Returns
    -------
    (already_selected, clicked) : tuple of Bool
        clicked is True if the item corresponding to the input event has
        just been clicked.
        already_selected indicates that the item corresponding to the
        input event is already selected.
    """
    raise NotImplementedError