old_contents: class HalfedgeMesh:
      def __init__(self, filename=None):
          """Make an empty halfedge mesh."""
          self.vertices = []
          self.halfedges = []
          self.facets = []
  
      def read_off(self, filename):
  
      class Vertex:
          def __init__(self, x, y, z, index):
              """Create a vertex with given index at given point.
  
              Args:
                  x: x-coordinate of the point
                  y: y-coordinate of the point
                  z: z-coordinate of the point
                  index: integer id of this vertex
              """
              pass
  
          def halfedges(self):
              """Return a list of halfedges targeting to this vertex."""
              pass
  
      class Facet:
          def __init__(self, index):
              """Create a facet with the given index."""
              pass
  
          def halfedges(self):
              """Return halfedges going ccw around this facet."""
              pass
  
      class Halfedge:
          def __init__(self, index):
              """Create a halfedge with given index."""
              pass
          def opposite(self):
              """Return the opposite halfedge."""
              pass
  
          def next(self):
              """Return the opposite halfedge."""
              pass
  
          def prev(self):
              """Return the opposite halfedge."""
              pass
  
          def vertex(self):
              """Return the target vertex."""
              pass
  
          def facet(self):
              """Return the incident facet."""
              pass
  
  
  if __name__ == '__main__':
      m = HalfedgeMesh()
  
new_contents: class HalfedgeMesh:
      def __init__(self, filename=None):
          """Make an empty halfedge mesh."""
          self.vertices = []
          self.halfedges = []
          self.facets = []
  
      def parse_off(self, filename):
          """Parses OFF files and returns a set of vertices, halfedges, and
          facets.
          """
          pass
  
      def get_halfedge(self, u, v):
          """Retrieve halfedge with starting vertex u and target vertex v
  
          u - starting vertex
          v - target vertex
  
          Returns a halfedge
          """
          pass
  
      class Vertex:
          def __init__(self, x, y, z, index):
              """Create a vertex with given index at given point.
  
              x     - x-coordinate of the point
              y     - y-coordinate of the point
              z     - z-coordinate of the point
              index - integer id of this vertex
              """
              pass
  
          def halfedges(self):
              """Return a list of halfedges targeting to this vertex."""
              pass
  
      class Facet:
          def __init__(self, index):
              """Create a facet with the given index."""
              pass
  
          def halfedges(self):
              """Return halfedges going ccw around this facet."""
              pass
  
      class Halfedge:
          def __init__(self, index):
              """Create a halfedge with given index."""
              pass
          def opposite(self):
              """Return the opposite halfedge."""
              pass
  
          def next(self):
              """Return the opposite halfedge."""
              pass
  
          def prev(self):
              """Return the opposite halfedge."""
              pass
  
          def vertex(self):
              """Return the target vertex."""
              pass
  
          def facet(self):
              """Return the incident facet."""
              pass
  
  
  if __name__ == '__main__':
      m = HalfedgeMesh()
  
subject: Add parse_off stub and change docstring