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._height*self._width

s = Screen() s.width = 1024 s.height = 768 print(s.resolution)

#assert s.resolution == 786432, '1024 * 768 = %d ?' % s.resolution