def _balance(self):
        if self.total is None:
            self.force_recalculate_total(save=True)
        return trunc_decimal(self.balance_paid-self.total, 2)
dataset/ETHPy150Open dokterbob/satchmo/satchmo/apps/satchmo_store/shop/models.py/Order._balance/swapped operands of `-`