Python class for subscribing data for several topics

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Hello all, I just get started with ros and now I am working with bagfiles and subscriber. Now I am trying to subscriber several topics from a bagfile using one node written in python. The following code is my attempt to achieve the aforementioned behavior. Nevertheless, this solution does not work. Someone can give me instruction on how I should create the python class ListenerVilma??? What are the best way to do this?

Thanks

#!/usr/bin/env python

import rospy
from rosgraph_msgs.msg import Clock
from diagnostic_msgs.msg import DiagnosticArray

class ListenerVilma:
    """Class that listens all topics of the file vilmafeagri"""

    def Clock_(self):
        """Method that listens the topic /clock if the file vilmafeagri"""
        def __init__(self):
            self.listener()


        def callback(self, clock):
            print clock


        def listener(self):
            rospy.Subscriber('clock', Clock, self.callback)


    def Diagnostics_(self):
        """Method that listen the topic /diagnostics from rosbag file vilmafeagri"""
        def __init__(self):
            self.listener()


        def callback(self, diagnostics):
            print diagnostics


        def listener(self):
            rospy.Subscriber('diagnostics', DiagnosticArray, self.callback)


if __name__ == '__main__':

    rospy.init_node('listener', anonymous=True)
    ListenerVilma.Clock_()
    rospy.spin()

The following performs better the behavior that I wanted. Now, the question is: Is this solution fast??? There better solutions???

class ListenerVilma:

def CLOCK(self):

    def clock_sub():
        rospy.Subscriber('clock', Clock, clock_callback)

    def clock_callback(clock):
        print clock

    clock_sub()


def DIAGNOSTICS(self):

    def diagnostics_sub():
        rospy.Subscriber('diagnostics', DiagnosticArray, diagnostics_callback)

    def diagnostics_callback(diagnostics):
        print diagnostics

    diagnostics_sub()

    if __name__ == '__main__':
        rospy.init_node('listener', anonymous=True)
        myVilma = ListenerVilma()
        myVilma.CLOCK()
        myVilma.DIAGNOSTICS()
        rospy.spin()