code: def derivation(self):
          
          drv = self.get('derivation')
          if drv is not None:
              if isinstance(drv, dict):
                  drv = Derivation.from_dict(drv)
              elif isinstance(drv, stringtypes):
                  drv = Derivation.from_string(drv)
          return drv
docs: Deserialize and return a Derivation object for UDF- or
          JSON-formatted derivation data; otherwise return the original
          string.