class Screen(object):

    @property

    def width(self):

        return self._width

    @width.setter

    def width(self,value):

        self._width=value

    @property

    def height(self):

        return self._height

    @height.setter

    def height(self,value):

        self._height=value      

    @property

    def resolution(self):

        self._resolution=self._width*self._height

        return self._resolution