How to use the pydot.Node function in pydot

---------------
    para : list or str
        if para is list, return itself, if para is str starts with "< " and
            follows by a file name, load the parameters in the txt

    Returns
        para : lsit
            a list of parameters
    --------------
    """
    if isinstance(para, str) and para.startswith('< '):
        f_name = para.split('< ')[0]
        return loadtxt(f_name)
    return para

class NNode(Node):
    """ Normal Node

    Parameters
    ---------------
    ipdests : list of str
        ip table for the node
    node_seq : int
        id of the node

    Attributes
    ----------------
    ipdests : list of str
        ip table for the node
    node_seq : int
        id of the node
    mod_num : int

}
        if use_urls:
            node_seed_shape = 'rectangle'
            node_shape = 'oval'
        else:
            node_seed_shape = 'square'
            node_shape = 'circle'
            node_args.update({
                "fixedsize": node_fixedsize,
                "width": node_width,
                "height": node_height,
            })

        graph.set_node_defaults(**node_args)
        for page in self.pages:
            graph.add_node(pydot.Node(name=self._clean_page_name(page, include_id=include_ids),
                                      fontname=fontname,
                                      fontsize=node_fontsize,
                                      shape=node_seed_shape if page.is_seed else node_shape))
            for link in page.links:
                graph.add_edge(pydot.Edge(self._clean_page_name(page, include_id=include_ids),
                                          self._clean_page_name(link, include_id=include_ids)))
        graph.write_png(filename)

def makeendnode(name):
    return pydot.Node(name, shape="doubleoctagon", label=name, 
        style="filled", fillcolor="#e4e4e4")

style = op_node_style
        # Check if we should override the style of this node.
        if styles is not None and op_node[0] in styles:
            style = styles[op_node[0]]
        pydot_graph.add_node(pydot.Node(op_node[0], **style, label="\n".join(op_node)))

    for data_node in data_nodes:
        pydot_graph.add_node(pydot.Node(data_node[0], label="\n".join(data_node[1:])))

    node_style = {'shape': 'oval',
                  'fillcolor': 'gray',
                  'style': 'rounded, filled'}

    if param_nodes is not None:
        for param_node in param_nodes:
            pydot_graph.add_node(pydot.Node(param_node[0], **node_style, label="\n".join(param_node[1:])))

    for edge in edges:
        pydot_graph.add_edge(pydot.Edge(edge[0], edge[1]))

    return pydot_graph

return self.py_dot_graph
		
		if self.__isCompartments():
			return self.py_dot_graph
			
		if self.__isSpecies():
			return self.py_dot_graph

		

		compart_dict = self.__createCompartmentDict()
		#Add the species into a compartment
		for i, sp in enumerate(self.m.getListOfSpecies()):
			node_attribute = self.specieNode(i+1)
			compart_dict[sp.getCompartment()][1].add_node(
				pydot.Node(sp.getId(), **node_attribute))
	
		for i, reaction in enumerate(self.m.getListOfReactions()):
			node_attribute = self.reactionNode(i+1)
			for j, sp_ref in enumerate(reaction.getListOfReactants()):
				if j == 0 and self.__addReactionToCompartment(sp_ref):
					compart_dict[sp.getCompartment()][1].add_node(
						pydot.Node(reaction.getId(), **node_attribute))
				
				# stoc = int(sp_ref.getStoichiometry()) # brett 20050702
				stoc = sp_ref.getStoichiometry() 		# brett 20050702: allow for non-int stoich
				
				edge_attribute = self.edgeNode(reaction, stoc).reactant()
				edge = pydot.Edge(sp_ref.getSpecies(), 
					reaction.getId(), **edge_attribute)
				self.add_edge(edge)

def buildNode(self,dimName,objtName):
    objtUrl = dimName + '#' + objtName
    if (dimName == 'persona'):
      objt = self.dbProxy.dimensionObject(objtName,'persona')
      if (objt.assumption() == True):
        objtLabel = "<<Assumption>>" + objtName
        self.theGraph.add_node(pydot.Node(objtName,label=objtLabel,shape='ellipse',fontname=self.fontName,fontsize=self.fontSize,URL=objtUrl))
      else:
        self.theGraph.add_node(pydot.Node(objtName,shape='ellipse',fontname=self.fontName,fontsize=self.fontSize,URL=objtUrl))
    elif (dimName == 'goalconcern' or dimName == 'taskconcern'):
      self.theGraph.add_node(pydot.Node(objtName,shape='note',fontname=self.fontName,fontsize=self.fontSize,fontcolor='blue',color='blue',URL=objtUrl))
    elif (dimName == 'obstacleconcern'):
      self.theGraph.add_node(pydot.Node(objtName,shape='note',fontname=self.fontName,fontsize=self.fontSize,fontcolor='red',color='red',URL=objtUrl))
    else:
      assetObjt = self.dbProxy.dimensionObject(objtName,dimName)
      borderColour = 'black'
      if (dimName == 'asset' and assetObjt.critical()):
        borderColour = 'red'
      if (dimName == 'template_asset' and self.isComponentAssetModel):
        stScore = self.dbProxy.templateAssetMetrics(objtName)
        assetNode = pydot.Node(objtName,shape='record',style='filled',fillcolor=surfaceTypeColourCode(stScore),fontcolor=surfaceTypeTextColourCode(stScore),fontname=self.fontName,fontsize=self.fontSize,URL=objtUrl)
      else:
        assetNode = pydot.Node(objtName,shape='record',color=borderColour,fontname=self.fontName,fontsize=self.fontSize,URL=objtUrl)
      self.theGraph.add_node(assetNode)
    self.nodeList.add(objtName)

def buildNode(self,dimName,objtName):
    objtUrl = dimName + '#' + str(objtName)
    if (dimName == 'task'):
      self.theGraph.add_node(pydot.Node(objtName,shape='ellipse',margin=0,fontname=self.fontName,fontsize=self.fontSize,URL=objtUrl))
    elif (dimName == 'domainproperty'):
      self.theGraph.add_node(pydot.Node(objtName,shape='house',margin=0,fontname=self.fontName,fontsize=self.fontSize,URL=objtUrl))
    elif (dimName == 'task_characteristic'):
      self.theGraph.add_node(pydot.Node(objtName,shape='record',margin=0,fontname=self.fontName,style='filled',fillcolor='green',fontsize=self.fontSize,URL=objtUrl))
    elif (dimName == 'rebuttal'):
      self.theGraph.add_node(pydot.Node(objtName,shape='record',margin=0,fontname=self.fontName,style='filled',fillcolor='red',fontcolor='white',fontsize=self.fontSize,URL=objtUrl))
    elif (dimName == 'qualifier'):
      self.theGraph.add_node(pydot.Node(objtName,shape='rectangle',margin=0,fontname=self.fontName,style='dashed',fontsize=self.fontSize,URL=objtUrl))
    elif (dimName == 'warrant'):
      self.theGraph.add_node(pydot.Node(objtName,shape='record',margin=0,fontname=self.fontName,style='filled',fillcolor='darkslategray3',fontsize=self.fontSize,URL=objtUrl))
    elif (dimName == 'backing'):
      self.theGraph.add_node(pydot.Node(objtName,shape='record',margin=0,fontname=self.fontName,style='filled',fillcolor='gray95',fontsize=self.fontSize,URL=objtUrl))
    elif (dimName == 'grounds'):
      self.theGraph.add_node(pydot.Node(objtName,shape='record',margin=0,fontname=self.fontName,fontsize=self.fontSize,URL=objtUrl))
    else: 
      self.theGraph.add_node(pydot.Node(objtName,shape='point',fontname=self.fontName,label='',fontsize=self.fontSize))

def makeendnode(name):
    name = escape_char(name, ':')
    return pydot.Node(name, shape="doubleoctagon", label=name, 
        style="filled", fillcolor="#e4e4e4")

def buildNode(self,objtName,envName):
    objtUrl = 'requirement#' + objtName
    envLabel = envName.replace(' ','_')
    if envName not in self.theClusters:
      self.theClusters[envName] = pydot.Cluster(envLabel,label=str(envName))
    reqObjt = self.dbProxy.dimensionObject(objtName,'requirement')
    tScore = self.dbProxy.traceabilityScore(objtName)
    fontColour = 'black'
    if (reqObjt.priority() == 1):
      if tScore != 3: fontColour = 1

    n = pydot.Node(objtName,color=str(tScore),fontcolor=str(fontColour),URL=objtUrl)
    if (self.cfSet == False):
      n.obj_dict['attributes']['style'] = '"rounded,filled"'
    self.theClusters[envName].add_node(n)

user_id = self._get_actor()

        try:
            import pydot
        except ImportError:
            raise ImportError("You need pydot library to get network functionality.")

        graph = pydot.Dot('network_of_user_{}'.format(user_id), graph_type='digraph')
        target_node = pydot.Node(user_id)

        for _id in self(user_id).following():
            user_node = pydot.Node(_id)
            graph.add_edge(pydot.Edge(target_node, user_node))

        for _id in self(user_id).followers():
            user_node = pydot.Node(_id)
            graph.add_edge(pydot.Edge(user_node, target_node))

        graph.write_png(output)