code: def add_node(self,node):
      
      if not isinstance(node, CondorDAGNode):
        raise CondorDAGError, "Nodes must be class CondorDAGNode or subclass"
      if not isinstance(node.job(), CondorDAGManJob):
        node.set_log_file(self.__log_file_path)
      self.__nodes.append(node)
      if self.__integer_node_names:
        node.set_name(str(self.__node_count))
      self.__node_count += 1
      if node.job() not in self.__jobs:
        self.__jobs.append(node.job())
docs: Add a CondorDAGNode to this DAG. The CondorJob that the node uses is
      also added to the list of Condor jobs in the DAG so that a list of the
      submit files needed by the DAG can be maintained. Each unique CondorJob
      will be added once to prevent duplicate submit files being written.
      @param node: CondorDAGNode to add to the CondorDAG.