Update with an ordered iterable of items.

        Args:
            iterable: An ordered iterable of items. The relative
               order of the items in this iterable will be respected
               in the TopoSet (in the absence of cycles).

def update(self, iterable):
        """Update with an ordered iterable of items.

        Args:
            iterable: An ordered iterable of items. The relative
               order of the items in this iterable will be respected
               in the TopoSet (in the absence of cycles).
        """
        for pair in pairwise_longest(iterable, fillvalue=_FILL):
            self._edges.append(pair)
            self._results = None