docs: def add_checkpoint_file(self,filename):
      """
      Add filename as a checkpoint file for this DAG node
      @param filename: checkpoint filename to add
      """
      if filename not in self.__checkpoint_files:
          self.__checkpoint_files.append(filename)
          if not isinstance(self.job(), CondorDAGManJob):
              if self.job().get_universe() == 'grid':
                  self.add_checkpoint_macro(filename)