class KinefxMultiSelection(object):
    def __init__(self):
        self._selections = []
        self._active_index = None

    def __getitem__(self, key):
        return self._selections[key]

    def __iter__(self):
        return iter(self._selections)

    def append(self, sel):
        if not isinstance(sel, KinefxSelection):
            raise TypeError("{} is not a KinefxSelection object".format(sel))
        self._selections.append(sel)

    def clear(self):
        # this class maintains the selection, so clear them individually
        # so that any other references also get emptied
        for s in self._selections:
            s.clear()
        self._selections.clear()