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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def verify_ethinca_metric_options(opts, parser):
 """ Checks that the necessary options are given for the ethinca metric calculation. Parameters opts : argparse.Values instance Result of parsing the input options with OptionParser parser : object The OptionParser instance. """

    if opts.filter_cutoff is not None and not (opts.filter_cutoff in
              pnutils.named_frequency_cutoffs.keys()):
        parser.error("Need a valid cutoff formula to calculate ethinca or "
                     "assign filter f_final values! Possible values are "
                     +str(pnutils.named_frequency_cutoffs.keys()))
    if (opts.calculate_ethinca_metric or opts.calculate_time_metric_components)\
                                           and not opts.ethinca_frequency_step:
        parser.error("Need to specify a cutoff frequency step to calculate "
                     "ethinca!")
    if not (opts.calculate_ethinca_metric or\
              opts.calculate_time_metric_components) and opts.ethinca_pn_order:
        parser.error("Can't specify an ethinca PN order if not "
                     "calculating ethinca metric!")