code: def edges(self):
          # TODO: check docstring
          
          for i in sorted(self._matrix.keys(), key=lambda x:x.name()):
              for j in sorted(self._matrix[i].keys(), key=lambda x:x.name()):
                  if i != j:
                      yield (i, j)
docs: Returns a generator for iterating over edges
          
          Yields
          ------
          type
              Generator for iterating over edges.