docs: def get_edge_pathways(self, edge_id):
          """Get the pathways associated with an edge.
  
          Parameters
          -----------
          edge_id : tup(int, int)
  
          Returns
          -----------
          tup(str, str)|None, the edge as a pair of 2 pathways if the edge id
            is in this network
          """
          vertex0_id, vertex1_id = edge_id
          pw0 = self.get_pathway_from_vertex_id(vertex0_id)
          pw1 = self.get_pathway_from_vertex_id(vertex1_id)
          if not pw0 or not pw1:
              return None
          return (pw0, pw1)