docs: def handler(self, value):
          """
          Setter for **self.__handler** attribute.
  
          :param value: Attribute value. ( SocketServer.BaseRequestHandler )
          """
  
          if value is not None:
              assert issubclass(value, SocketServer.BaseRequestHandler), \
                  "'{0}' attribute: '{1}' is not 'SocketServer.BaseRequestHandler' subclass!".format("handler", value)
          self.__handler = value
          self.__handler.container = self