def __isub__(self, other):
        if isinstance(other, self.__class__):
            self.standard -= other.standard
            return self
        else:
            raise TypeError({"class":pretty_name(self)} % '%(class)s must be subtracted from %(class)s')
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.5/django/contrib/gis/measure.py/MeasureBase.__isub__/swapped operands of `%`