Callback doen't respond

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I have the following node :

    def set_set_goal_pose_callback(pose,em):
        print "i am here", pose.pose.position.x
    def listener()
        em=ratslam.experience_map_younes.ExperienceMap()
        sub_goal=rospy.Subscriber("/ExperienceMap/RobotPose",PoseStamped,set_goal_pose_callback,em)
        rospy.spin()

   if __name__=='__main__':
        rospy.init_node("RatSLAMExperienceMap')
        listener()

When I execute the node, the function set_goal_pose_callback isn't called. What could I do?