code: def extract_edges(self, feature_angle=30, boundary_edges=True,
                        non_manifold_edges=True, feature_edges=True,
                        manifold_edges=True, inplace=False):
          
          surf = self.extract_surface()
          return surf.extract_edges(feature_angle, boundary_edges,
                                    non_manifold_edges, feature_edges,
                                    manifold_edges, inplace=inplace)
docs: Extracts edges from the surface of the grid.  From vtk documentation:
  
          These edges are either
              1) boundary (used by one polygon) or a line cell;
              2) non-manifold (used by three or more polygons)
              3) feature edges (edges used by two triangles and whose
                 dihedral angle > feature_angle)
              4) manifold edges (edges used by exactly two polygons).
  
          Parameters
          ----------
          feature_angle : float, optional
              Defaults to 30 degrees.
  
          boundary_edges : bool, optional
              Defaults to True
  
          non_manifold_edges : bool, optional
              Defaults to True
  
          feature_edges : bool, optional
              Defaults to True
  
          manifold_edges : bool, optional
              Defaults to True
  
          inplace : bool, optional
              Return new mesh or overwrite input.
  
          Returns
          -------
          edges : vtki.vtkPolyData
              Extracted edges