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):

        return self._width * self._height

s = Screen()

s.width = 1024

s.height = 768

print(s.resolution)