class Screen(object): @property def width(self): return self._width @width.setter def width(self,value): if not isinstance(value,int): raise ValueError('width must be number!') self._width=value @property def height(self): return self._height @height.setter def height(self,value): if not isinstance(value,int): raise ValueError('height must be number!') self._height=value @property def resolution(self): return self._width*self._height