Print the graph for self's nodes.

        Args:
            format (str): output format (csv, json or text).
            output (file): file descriptor on which to write.
            depth (int): depth of the graph.

def print_graph(self, format=None, output=sys.stdout, depth=0, **kwargs):
        """
        Print the graph for self's nodes.

        Args:
            format (str): output format (csv, json or text).
            output (file): file descriptor on which to write.
            depth (int): depth of the graph.
        """
        graph = self.as_graph(depth=depth)
        graph.print(format=format, output=output, **kwargs)