new_contents: from __future__ import print_function
  from __future__ import absolute_import
  from time import sleep
  
  from .vnrpc import RpcClient
  
  
  class TestClient(RpcClient):
      """
      Test RpcClient   
      """   
      def __init__(self, req_address, sub_address):
          """
          Constructor
          """
          super(TestClient, self).__init__(req_address, sub_address)
  
      def callback(self, topic, data):
          """
          Realize callable function
          """
          print('client received topic:', topic, ', data:', data)
  
  
  if __name__ == '__main__':
      req_address = 'tcp://localhost:2014'
      sub_address = 'tcp://localhost:0602'
  
      tc = TestClient(req_address, sub_address)
      tc.subscribeTopic('')
      tc.start()
  
      while 1:
          print(tc.add(1, 3))
          sleep(2)
  
subject: Create test_client.py