code: def hub(self, port):
          ''' java -jar selenium-server.jar -role hub -port 4444
          @param port:  listen port of selenium hub 
          '''
          self._ip = "localhost"
          self._port = port 
          self.command = [self._conf["java_path"], "-jar", self._conf["jar_path"], "-port", str(port), "-role", "hub"]        
          return self hub(self, port):
          ''' java -jar selenium-server.jar -role hub -port 4444
          @param port:  listen port of selenium hub 
          '''
          self._ip = "localhost"
          self._port = port 
          self.command = [self._conf["java_path"], "-jar", self._conf["jar_path"], "-port", str(port), "-role", "hub"]        
          return self
docs: java -jar selenium-server.jar -role hub -port 4444
          @param port:  listen port of selenium hub