Setter for **self.__handler** attribute.

        :param value: Attribute value. ( SocketServer.BaseRequestHandler )

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