class Screen(object): @property def width(self): return self._width @property def height(self): return self._height @property def resolution(self): return self._width*self._height @width.setter def width(self,value): if not isinstance(value,int): raise ValueError('width is a int') if value<=0: raise ValueError('width is greater than 0') self._width=value @height.setter def height(self,value): if not isinstance(value,int): raise ValueError('height is a int') if value<=0: raise ValueError('height is greater than 0') self._height=value