Does rospy have a get_subscribed_topics() function?

edit

This code should help accomplish what you want. It will simply print out the entire ROSGraph nodes and edges. You can infer subscribers from here.

 #!/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
if __name__ == '__main__':
    try:
        mygraph()
    except rospy.ROSInterruptException: pass