code: def request_sensor_value(self, req, msg):
          
          exact, name_filter = construct_name_filter(msg.arguments[0]
                                                     if msg.arguments else None)
          sensors = [(name, sensor) for name, sensor in
                     sorted(self._sensors.iteritems()) if name_filter(name)]
  
          if exact and not sensors:
              return req.make_reply("fail", "Unknown sensor name.")
  
          katcp_version = self.PROTOCOL_INFO.major
          for name, sensor in sensors:
              timestamp, status, value = sensor.read_formatted(katcp_version)
              req.inform(timestamp, "1", name, status, value)
          return req.make_reply("ok", str(len(sensors)))
docs: Request the value of a sensor or sensors.
  
          A list of sensor values as a sequence of #sensor-value informs.
  
          Parameters
          ----------
          name : str, optional
              Name of the sensor to poll (the default is to send values for all
              sensors). If name starts and ends with '/' it is treated as a
              regular expression and all sensors whose names contain the regular
              expression are returned.
  
          Informs
          -------
          timestamp : float
              Timestamp of the sensor reading in seconds since the Unix
              epoch, or milliseconds for katcp versions <= 4.
          count : {1}
              Number of sensors described in this #sensor-value inform. Will
              always be one. It exists to keep this inform compatible with
              #sensor-status.
          name : str
              Name of the sensor whose value is being reported.
          value : object
              Value of the named sensor. Type depends on the type of the sensor.
  
          Returns
          -------
          success : {'ok', 'fail'}
              Whether sending the list of values succeeded.
          informs : int
              Number of #sensor-value inform messages sent.
  
          Examples
          --------
          ::
  
              ?sensor-value
              #sensor-value 1244631611.415231 1 psu.voltage 4.5
              #sensor-value 1244631611.415200 1 cpu.status off
              ...
              !sensor-value ok 5
  
              ?sensor-value cpu.power.on
              #sensor-value 1244631611.415231 1 cpu.power.on 0
              !sensor-value ok 1