code: def verify_fft_options(opt,parser):
      
      if opt.fftw_measure_level not in [0,1,2,3]:
          parser.error("{0} is not a valid FFTW measure level.".format(opt.fftw_measure_level))
  
      if opt.fftw_import_system_wisdom and ((opt.fftw_input_float_wisdom_file is not None)
                                            or (opt.fftw_input_double_wisdom_file is not None)):
          parser.error("If --fftw-import-system-wisdom is given, then you cannot give"
                       " either of --fftw-input-float-wisdom-file or --fftw-input-double-wisdom-file")
  
      if opt.fftw_threads_backend is not None:
          if opt.fftw_threads_backend not in ['openmp','pthreads','unthreaded']:
              parser.error("Invalid threads backend; must be 'openmp', 'pthreads' or 'unthreaded'")
docs: Parses the FFT options and verifies that they are
         reasonable.
  
      Parameters
      ----------
      opt : object
          Result of parsing the CLI with OptionParser, or any object with the
          required attributes.
      parser : object
          OptionParser instance.