def __sub__(self, other):
        if isinstance(other, Area):
            return Area(default_unit=self._default_unit, sq_m=(self.sq_m - other.sq_m))
        else:
            raise TypeError('Area must be subtracted from Area')
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.2/django/contrib/gis/measure.py/Area.__sub__/original