code: def add_var_arg(self, arg):
      
      self.__args.append(arg)
      self.__job.add_var_arg(self.__arg_index)
      self.__arg_index += 1
docs: Add a variable (or macro) argument to the condor job. The argument is
      added to the submit file and a different value of the argument can be set
      for each node in the DAG.
      @param arg: name of option to add.