code: def heater_level(self, value):
          
          if self._ext_sw_heater_drive:
              if value not in range(0, self._heater_bangbang_segments+1):
                  raise exceptions.RoasterValueError
              self._heater_level.value = value
          else:
              raise exceptions.RoasterValueError
docs: Verifies that the heater_level is between 0 and heater_segments.
             Can only be called when freshroastsr700 object is initialized
             with ext_sw_heater_drive=True. Will throw RoasterValueError
             otherwise.