Using Rostopic hz in a ros node

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I think I was struggling with this problem because I am not familiar with Python, but it wasn't too hard after reading the rostopic source code for a couple of hours.

I also encountered problems with rostopic hz because I did not have a list of topic names beforehand. Run the sample ros node below to understand how to retrieve all of this data. The myhz() method will run the ros loop and continuously print out the rate of the sometopic, and the mygraph() function will print all nodes and edges (with to and from information).

#!/usr/bin/env python import roslib; 
    roslib.load_manifest('ssnode') import 
    rospy import roslib 
    import roslib.message
    import rosgraph
    import rostopic 
    from rostopic import ROSTopicHz 
    from rosgraph.impl import graph

    def mygraph():
        g = graph.Graph()
        try:
            while 1:
              g.update()

              if not g.nn_nodes and not g.srvs:
                  print("empty")
              else:
                  print('\n')
              if g.nn_nodes:
                  print('Nodes:')
                  for n in g.nn_nodes:
                      prefix = n + '|'
                      print('  ' + n + ' :')
                      print('    Inbound:')
                      for k in g.nn_edges.edges_by_end.iterkeys():
                          if k.startswith(prefix):
                              for c in g.nn_edges.edges_by_end[k]:
                                  print('      ' + c.start + ' label = '
+ c.label)
                      print('    Outbound:')
                      for k in g.nn_edges.edges_by_start.iterkeys():
                          if k.startswith(prefix):
                              for c in g.nn_edges.edges_by_start[k]:
                                  print('      ' + c.end + ' label = ' + c.label)
              if g.srvs:
                  print('Services:')
                  for s in g.srvs:
                      print('  ' + s)
        except KeyboardInterrupt:
            pass

             def myhz(topic, window_size=-1, filter_expr=None):
        rospy.loginfo("check if roscore is up")
        while !rospy.is_shutdown():         thegraph();         ros::sleep(10);
            return
        rospy.init_node("myname", anonymous=True)
        rospy.loginfo("registered node name")
        rt = ROSTopicHz(window_size, filter_expr=filter_expr)

        # have to subscribe with topic_type
        sub = rospy.Subscriber(topic, rospy.AnyMsg, rt.callback_hz)        
        print("subscribed to [%s]"%topic)
        while not rospy.is_shutdown():
            rospy.loginfo(rt.times)


    if __name__ == '__main__':
        try:
          mygraph()
          #myhz("sometopic")
        except rospy.ROSInterruptException: pass