Oscar's structured strategy with min/max prices

strategy.py

from collections import namedtuple
from operator import attrgetter
from oscar.apps.partner import prices
from oscar.apps.partner.strategy import Structured


# A container for policies
ExtendedPurchaseInfo = namedtuple(
    'ExtendedPurchaseInfo', ['price',
                             'min_price',
                             'max_price',
                             'availability',
                             'stockrecord'])


class StructuredWithMinMax(Structured):
    def fetch_for_product(self, product, stockrecord=None):
        if stockrecord is None:
            stockrecord = self.select_stockrecord(product)
        price = self.pricing_policy(product, stockrecord)
        min_price = max_price = prices.Unavailable()

        return ExtendedPurchaseInfo(
            price=price,
            min_price=min_price,
            max_price=max_price,
            availability=self.availability_policy(product, stockrecord),
            stockrecord=stockrecord)

    def fetch_for_parent(self, product):
        children_stock = self.select_children_stockrecords(product)
        price = self.parent_pricing_policy(product, children_stock)

        stockrecords = [x[1] for x in children_stock if x[1] is not None]
        if stockrecords:
            cheap_children_stockrecord = min(stockrecords, key=attrgetter('price_excl_tax'))
            expensive_children_stockrecord = max(stockrecords, key=attrgetter('price_excl_tax'))
            min_price = self.pricing_policy(product, cheap_children_stockrecord)
            max_price = self.pricing_policy(product, expensive_children_stockrecord)
        else:
            min_price = max_price = prices.Unavailable()

        return ExtendedPurchaseInfo(
            price=price,
            min_price=min_price,
            max_price=max_price,
            availability=self.parent_availability_policy(product, children_stock),
            stockrecord=None)