def valid(self, order=None):
        if order:
            quants = [item.quantity for item in order.orderitem_set.all() if item.product.is_shippable]
            if quants:
                qty = reduce(operator.add, quants)
            else:
                qty = Decimal('0')
                                                
        elif self.cart:
            qty = self.cart.numItems

        try:
            price = self.carrier.price(qty)
            
        except TieredPriceException:
            return False
                        
        return True
Check to see if this order can be shipped using this method
dataset/ETHPy150Open dokterbob/satchmo/satchmo/apps/shipping/modules/tieredquantity/models.py/Shipper.valid