Octomap_msg in Python not working

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I am trying to load octomap processed from another node to a node subscribed in python. I have used the octomap_msgs/conversion.h to convert the octomap to msg (fullMapToMsg). But I am not able to read the msg in Python subscriber. Please guide me . The code for subscriber is as follows

#!/usr/bin/env python
import rospy
from octomap_msgs.msg import Octomap

def callback(map_msg):
    print "recieved"


def main():
    print "initializing node"
    rospy.init_node('process_data',anonymous = True)
    print "Subcribing nodes"    
    rospy.Subscriber("/oct_msg",Octomap,callback)
    print "finished"
    rospy.spin()


if __name__=='__main__':
    main()

The output is :

initializing node
Subcribing nodes
finished