code: def edges(self):
          
          edges, index = geometry.faces_to_edges(self.faces.view(np.ndarray),
                                                 return_index=True)
          self._cache['edges_face'] = index
          return edges
docs: Edges of the mesh (derived from faces).
  
          Returns
          ---------
          edges : (n, 2) int
            List of vertex indices making up edges