code: def unpack(self, packed_value, major=DEFAULT_KATCP_MAJOR):
          
          if packed_value is None:
              value = self.get_default()
          else:
              try:
                  value = self.decode(packed_value, major)
              except Exception:
                  raise
          if value is not None:
              self.check(value, major)
          return value
docs: Parse a KATCP parameter into an object.
  
          Parameters
          ----------
          packed_value : str
              The unescaped KATCP string to parse into a value.
          major : int, optional
              Major version of KATCP to use when interpreting types.
              Defaults to latest implemented KATCP version.
  
          Returns
          -------
          value : object
              The value the KATCP string represented.