<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def flip_ctrlpts2d_file(file_in='', file_out='ctrlpts_flip.txt'):
 """ 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 """

    # 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)