How to use the visualdl.server.graphviz_graph.Graph function in visualdl

def rank_group(self, kind, priority):
        name = "rankgroup-%d" % Graph.rank_counter
        Graph.rank_counter += 1
        rank = Rank(kind, name, priority)
        self.rank_groups[name] = rank
        return name

'''
        self.source = source
        self.target = target
        self.attrs = attrs

    def __str__(self):
        repr = "{source} -> {target} {extra}".format(
            source=self.source.name,
            target=self.target.name,
            extra="" if not self.attrs else
            "[" + ','.join("{}={}".format(attr[0], crepr(attr[1]))
                           for attr in self.attrs.items()) + "]")
        return repr


g_graph = Graph(title="some model")


def add_param(label, graph=None):
    if not graph:
        graph = g_graph
    return graph.node(label=label, prefix='param', color='blue')


def add_op(label, graph=None):
    if not graph:
        graph = g_graph
    label = '\n'.join([
        '',
        '  ',
        '    <table border="0"><tbody><tr><td>',
        label,</td></tr></tbody></table>