class Screen(object):

@property
def width(self):
    return self._width

@width.setter
def width(self, value):
    if not isinstance(value, (int, float)):
        raise ValueError('width must be a number')
    if value <= 0:
        raise ValueError('width must be more than zero')
    self._width = value

@property
def height(self):
    return self._height

@height.setter
def height(self, value):
    if not isinstance(value, (int, float)):
        raise ValueError('height must be a number')
    if value <= 0:
        raise ValueError('height must be more than zero')
    self._height = value

@property
def resolution(self):
    return self._width * self._height