def _parse_face(face_row):
  """Parses a line in a PLY file which encodes a face of the mesh."""
  face = [int(index) for index in face_row.strip().split()]
  # Assert that number of vertices in a face is 3, i.e. it is a triangle
  if len(face) != 4 or face[0] != 3:
    raise ValueError(
      'Only supports face representation as a string with 4 numbers.')

  return face[1:]