How to use the whisper.setXFilesFactor function in whisper

# Other header information should not change
        self.assertEqual(info0['aggregationMethod'],
                         info1['aggregationMethod'])
        self.assertEqual(info0['maxRetention'], info1['maxRetention'])
        self.assertEqual(info0['archives'], info1['archives'])

        # packing and unpacking because
        # AssertionError: 0.20000000298023224 != 0.2
        target_xff = struct.unpack("!f", struct.pack("!f", target_xff))[0]
        self.assertEqual(info1['xFilesFactor'], target_xff)

        with AssertRaisesException(
            whisper.InvalidXFilesFactor('Invalid xFilesFactor zero, not a '
                                        'float')):
            whisper.setXFilesFactor(self.filename, "zero")

        for invalid_xff in -1, 2:
            with AssertRaisesException(
                whisper.InvalidXFilesFactor('Invalid xFilesFactor %s, not '
                                            'between 0 and 1' %
                                            float(invalid_xff))):
                whisper.setXFilesFactor(self.filename, invalid_xff)

# packing and unpacking because
        # AssertionError: 0.20000000298023224 != 0.2
        target_xff = struct.unpack("!f", struct.pack("!f", target_xff))[0]
        self.assertEqual(info1['xFilesFactor'], target_xff)

        with AssertRaisesException(
            whisper.InvalidXFilesFactor('Invalid xFilesFactor zero, not a '
                                        'float')):
            whisper.setXFilesFactor(self.filename, "zero")

        for invalid_xff in -1, 2:
            with AssertRaisesException(
                whisper.InvalidXFilesFactor('Invalid xFilesFactor %s, not '
                                            'between 0 and 1' %
                                            float(invalid_xff))):
                whisper.setXFilesFactor(self.filename, invalid_xff)

def test_set_xfilesfactor(self):
        """
        Create a whisper file
        Update xFilesFactor
        Check if update succeeded
        Check if exceptions get raised with wrong input
        """
        whisper.create(self.filename, [(1, 20)])

        target_xff = 0.42
        info0 = whisper.info(self.filename)
        old_xff = whisper.setXFilesFactor(self.filename, target_xff)
        # return value should match old xff
        self.assertEqual(info0['xFilesFactor'], old_xff)
        info1 = whisper.info(self.filename)

        # Other header information should not change
        self.assertEqual(info0['aggregationMethod'],
                         info1['aggregationMethod'])
        self.assertEqual(info0['maxRetention'], info1['maxRetention'])
        self.assertEqual(info0['archives'], info1['archives'])

        # packing and unpacking because
        # AssertionError: 0.20000000298023224 != 0.2
        target_xff = struct.unpack("!f", struct.pack("!f", target_xff))[0]
        self.assertEqual(info1['xFilesFactor'], target_xff)

        with AssertRaisesException(

def main():
    """Set xFilesFactor for existing whisper file"""
    parser = argparse.ArgumentParser(
        description='Set xFilesFactor for existing whisper file')
    parser.add_argument('path', type=str, help='path to whisper file')
    parser.add_argument('xff', metavar='xFilesFactor', type=float,
                        help='new xFilesFactor, a float between 0 and 1')

    args = parser.parse_args()

    try:
        old_xff = whisper.setXFilesFactor(args.path, args.xff)
    except IOError:
        sys.stderr.write("[ERROR] File '%s' does not exist!\n\n" % args.path)
        parser.print_help()
        sys.exit(1)
    except whisper.WhisperException as exc:
        raise SystemExit('[ERROR] %s' % str(exc))

    print('Updated xFilesFactor: %s (%s -> %s)' %
          (args.path, old_xff, args.xff))