code: def timestamp(cls, name, description=None, unit='',
                    default=None, initial_status=None):
          
          return cls(cls.TIMESTAMP, name, description, unit, None,
                     default, initial_status)
docs: Instantiate a new timestamp sensor object.
  
          Parameters
          ----------
          name : str
              The name of the sensor.
          description : str
              A short description of the sensor.
          units : str
              The units of the sensor value. For timestamp sensor may only be the
              empty string.
          default : string
              An initial value for the sensor in seconds since the Unix Epoch.
              Defaults to 0.
          initial_status : int enum or None
              An initial status for the sensor. If None, defaults to
              Sensor.UNKNOWN. `initial_status` must be one of the keys in
              Sensor.STATUSES