code: def temperature_series(self, unit='kelvin'):
          
          if unit not in ('kelvin', 'celsius', 'fahrenheit'):
              raise ValueError("Invalid value for parameter 'unit'")
          result = []
          for tstamp in self._station_history.get_measurements():
              t = self._station_history.get_measurements()[tstamp]['temperature']
              if unit == 'kelvin':
                  temp = t
              if unit == 'celsius':
                  temp = temputils.kelvin_to_celsius(t)
              if unit == 'fahrenheit':
                  temp = temputils.kelvin_to_fahrenheit(t)
              result.append((tstamp, temp))
          return result
docs: Returns the temperature time series relative to the meteostation, in
          the form of a list of tuples, each one containing the couple
          timestamp-value
  
          :param unit: the unit of measure for the temperature values. May be
              among: '*kelvin*' (default), '*celsius*' or '*fahrenheit*'
          :type unit: str
          :returns: a list of tuples
          :raises: ValueError when invalid values are provided for the unit of
              measure