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

def __setitem__(self, key, value, dict_setitem=dict.__setitem__, proxy=_proxy, Link=_Link):

    if (key not in self):
        self.__map[key] = link = Link()
        root = self.__root
        last = root.prev
        (link.prev, link.next, link.key) = (last, root, key)
        last.next = link
        root.prev = proxy(link)
    dict_setitem(self, key, value)
