code: def update(self, iterable):
          
          for pair in pairwise_longest(iterable, fillvalue=_FILL):
              self._edges.append(pair)
              self._results = None
docs: 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).