code: def _init_edges_relationships(rel2src2dsts, rel2dst2srcs):
          
          edge_rel2fromto = {}
          relationships = set(rel2src2dsts).union(rel2dst2srcs)
          for reltype in relationships:
              edge_from_to = []
              if reltype in rel2src2dsts:
                  for parent, children in rel2src2dsts[reltype].items():
                      for child in children:
                          edge_from_to.append((child, parent))
              if reltype in rel2dst2srcs:
                  for parent, children in rel2dst2srcs[reltype].items():
                      for child in children:
                          edge_from_to.append((child, parent))
              edge_rel2fromto[reltype] = edge_from_to
          return edge_rel2fromto
docs: Get the directed edges from GO term to GO term using relationships.