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