code

    SampleRateUnit = {'Seconds': '0', 'Minutes': '1', 'Hours': '2',
                      'Days': '3', '%': '4'}
    SamplePeriodUnit = {'Seconds': '0', 'Minutes': '1', 'Hours': '2',
                        'Days': '3', 'Weeks': '4', 'Pulses': '5'}
    TotalDurationUnit = {'Period': '0', 'Seconds': '1', 'Minutes': '2',
                         'Hours': '3', 'Days': '4', 'Weeks': '5', 'Continuous': '6',
                                'predefinded': '7'}
    TimeStampEnabled = {False: 0, True: 1}

    @Feat(values=(None, SampleRateUnit, None, SamplePeriodUnit, None,
                  TotalDurationUnit, TimeStampEnabled,))
    def sampling(self):
        """This command is used to read the current data sampling settings.
        (rds)
        """
        return self.parse_query('*rds', format='Sample Rate: {:f} / {}\t'
                                               'Sample Period: {:f} / {}\t'
                                               'Total Duration: {:f} {}\t'
                                               'Time Stamp: {}')

    @sampling.setter
    def sampling(self, value):
        """This command provides the data sampling parameters for the logging
        and statistics environments. (dsu)
        """
        self.query('*dsu {} {} {} {} {} {} {}'.format(*value))

previous code returns:

14:47:04 INFO Getting sampling
14:47:04 DEBUG Sending b'*rds\r\n'
14:47:04 DEBUG Received 'Sample Rate: 1 / Seconds\tSample Period: 30 / Minutes\tTotal Duration: 1 Period\tTime Stamp: ON\r\n' (len=94)
14:47:04 DEBUG (raw) Got [1, 'Seconds', 30, 'Minutes', 1, 'Period', 'ON'] for sampling
14:47:04 ERROR While post-processing [1, 'Seconds', 30, 'Minutes', 1, 'Period', 'ON'] for sampling: 'Seconds' not in ('4', '2', '3', '0', '1')
14:47:04 DEBUG Closing port /dev/ttyUSB0
Traceback (most recent call last):
File "842PE.py", line 404, in
print(inst.sampling)
File "/usr/lib/python3.3/site-packages/Lantz-0.3.dev0-py3.3.egg/lantz/feat.py", line 303, in get
return self.get(instance)
File "/usr/lib/python3.3/site-packages/Lantz-0.3.dev0-py3.3.egg/lantz/feat.py", line 255, in get
raise e
File "/usr/lib/python3.3/site-packages/Lantz-0.3.dev0-py3.3.egg/lantz/feat.py", line 252, in get
value = self.post_get(value, instance, key)
File "/usr/lib/python3.3/site-packages/Lantz-0.3.dev0-py3.3.egg/lantz/feat.py", line 213, in post_get
value = processor(value)
File "/usr/lib/python3.3/site-packages/Lantz-0.3.dev0-py3.3.egg/lantz/processors.py", line 169, in call
for processor, value in zip(self.processors, values))
File "/usr/lib/python3.3/site-packages/Lantz-0.3.dev0-py3.3.egg/lantz/processors.py", line 169, in
for processor, value in zip(self.processors, values))
File "/usr/lib/python3.3/site-packages/Lantz-0.3.dev0-py3.3.egg/lantz/processors.py", line 403, in _inner
raise ValueError("{!r} not in {}".format(key, tuple(container.keys())))
ValueError: 'Seconds' not in ('4', '2', '3', '0', '1')

As one can see, there is no need for conversion in the getter as the return from the device is already in the correct form (except 'ON' -> True). Maybe it's just easyer to not make a getter/setter for this one.

I see now. Sorry for the confusion. In this cases where the instrument programming code is not designed in a simmetrical way, you can still use getter and setter but just avoid the automatic conversion using values.

SampleRateUnit = {'Seconds': '0', 'Minutes': '1', 'Hours': '2',
                  'Days': '3', '%': '4'}
SamplePeriodUnit = {'Seconds': '0', 'Minutes': '1', 'Hours': '2',
                    'Days': '3', 'Weeks': '4', 'Pulses': '5'}
TotalDurationUnit = {'Period': '0', 'Seconds': '1', 'Minutes': '2',
                     'Hours': '3', 'Days': '4', 'Weeks': '5', 'Continuous': '6',
                     'predefinded': '7'}
TimeStampEnabled = {False: 0, True: 1}

@Feat(values=(None, SampleRateUnit, None, SamplePeriodUnit, None,
              TotalDurationUnit, TimeStampEnabled,))
def sampling(self):
    """This command is used to read the current data sampling settings.
    (rds)
    """
    out = self.parse_query('*rds', format='Sample Rate: {} / {}\t'
                           'Sample Period: {} / {}\t'
                           'Total Duration: {} {}\t'
                           'Time Stamp: {}')
    out[0] = int(out[0])
    out[2] = int(out[2])
    out[4] = int(out[4])
    out[6] = True if value[6] == 'ON' else False
    return out

@sampling.setter
def sampling(self, value):
    """This command provides the data sampling parameters for the logging
    and statistics environments. (dsu)
    """
    value[1] = self.SamplePeriodUnit[value[1]]
    value[3] = self.SamplePeriodUnit[value[3]]
    value[5] = self.TotalDurationUnit[value[5]]
    value[6] = 1 if value[6] else 0
    self.query('*dsu {} {} {} {} {} {} {}'.format(*value))

By the way, are you sure that the numbers are always integers?