code: def get_edges(self):
          
          edge_from_to = []
          for parent, children in self.p_from_cs.items():
              for child in children:
                  edge_from_to.append((child, parent))
          for parent, children in self.c_from_ps.items():
              for child in children:
                  edge_from_to.append((child, parent))
          return edge_from_to
docs: Get the directed edges from GO term to GO term.