code: def get_objective_banks(self):
          
          if self.retrieved:
              raise errors.IllegalState('List has already been retrieved.')
          self.retrieved = True
          return objects.ObjectiveBankList(self._results, runtime=self._runtime)
docs: Gets the objective bank list resulting from the search.
  
          return: (osid.learning.ObjectiveBankList) - the objective bank
                  list
          raise:  IllegalState - list already retrieved
          *compliance: mandatory -- This method must be implemented.*