code: def flip_ctrlpts2d_file(file_in='', file_out='ctrlpts_flip.txt'):
      
      # Read control points
      ctrlpts2d, size_u, size_v = _read_ctrltps2d_file(file_in)
  
      # Flip control points array
      new_ctrlpts2d = flip_ctrlpts2d(ctrlpts2d, size_u, size_v)
  
      # Save new control points
      _save_ctrlpts2d_file(new_ctrlpts2d, size_u, size_v, file_out)
docs: Flips u and v directions of a 2D control points file and saves flipped coordinates to a file.
  
      :param file_in: name of the input file (to be read)
      :type file_in: str
      :param file_out: name of the output file (to be saved)
      :type file_out: str
      :raises IOError: an error occurred reading or writing the file