cart.py

class ShoppingCart(object):
    def __init__(self):
        self.items=[]
    def add(self,item,price):
        for cart_item in self.items:
            if cart_item.item == item:
                cart_item.q+=1
                return self
        self.items.append(Item(item,price))
        return self
    def item(self,index):
        return self.items[index-1].item
    def price(self,index):
        return self.items[index-1].price*self.items[index-1].q
    def total(self,sales_tax):
        sum_price=sum([item.price*item.q for item in self.items])
        return sum_price*(1.0+sales_tax/100.0)
    def __len__(self):
        return sum([item.q for item in self.items])
class Item(object):
    def __init__(self,item,price,q=1):
        self.item=item
        self.price=price
        self.q=q