code: def unpack(self, value):
          
          # Wrap errors in FailReplies with information identifying the parameter
          try:
              return self._kattype.unpack(value, self.major)
          except ValueError, message:
              raise FailReply("Error in parameter %s (%s): %s" %
                              (self.position, self.name, message))
docs: Unpack the parameter using its kattype.
  
          Parameters
          ----------
          packed_value : str
              The unescaped KATCP string to unpack.
  
          Returns
          -------
          value : object
              The unpacked value.