'od.__setitem__(i, y) <==> od[i]=y'

def __setitem__(self, key, value, PREV=0, NEXT=1, dict_setitem=dict.__setitem__):

    if (key not in self):
        root = self.__root
        last = root[PREV]
        last[NEXT] = root[PREV] = self.__map[key] = [last, root, key]
    dict_setitem(self, key, value)
