class Screen(object):

    @property

    def width(self):

        return self._width

    @width.setter

    def width(self, value):

        if not isinstance(value, float):

            raise ValueError('score must be an floater!')

        if value < 0 or value > 100:

            raise ValueError('score must between 0 ~ 100!')

        self._width = value

    @property

    def height(self):

        return self._height

    @height.setter

    def height(self, value):

        if not isinstance(value, float):

            raise ValueError('score must be an floater!')

        if value < 0 or value > 100:

            raise ValueError('score must between 0 ~ 100!')

        self._height = value

    @property

    def resolution(self):

        return self._width * self._height

s = Screen()

s.width = 24.2

s.height = 18.9

s.resolution

457.37999999999994