如何修改列表中项目的数量？

Question

对于一些信息，我基本上必须创建 2 个名为 ItemToPurchase 的类，其中包含商品的名称、数量、描述和价格。 另一个 class ShoppingCart 将商品名称添加到列表中。 现在，我很难修改列表中某个项目的数量，因为它一直告诉我在购物车中找不到该项目。

class ItemToPurchase:
    def __init__(self):
        self.name = 'none'
        self.quantity = 0
        self.price = 0
        self.description = 'none'

    def item_name(self, name):
        self.name = name

    def item_price(self, price):
        self.price = price

    def item_quantity(self, quantity):
        self.quantity = quantity

    def item_description(self, description):
        self.description = description

    def print_item_cost(self):
        print(self.name + " " + str(self.quantity) + " @ $" + str(self.price) + " = $" + str(int(self.quantity) * int(self.price)))

    def print_item_description(self):
        print(self.name + ": " + self.description)

class ShoppingCart:
    def __init__(self, name='none', date='January 1, 2016'):
        self.customer_name = name
        self.current_date = date
        self.cart_items = []

    def add_item(self, New_cart):
        self.cart_items.append(New_cart)

    def remove_item(self, item_name):
        count = 0
        items = self.cart_items[:]
        for i in range(len(items)):
            item = items[i]
            if item.name == item_name:
                del self.cart_items[i]
                count += 1
        if count == 0:
            print()
            print('Item not found in cart. Nothing removed')
            
    **def modify_item(self, ItemToPurchase, Item_Name):
        num = 0
        items = self.cart_items[:]
        for i in range(len(items)):
            item = items[i]
            if Item_Name in items:
                num += 1
                if ItemToPurchase.description != "none":
                    item.item_description(ItemToPurchase.description)
                if ItemToPurchase.price != 0:
                    item.item_price(ItemToPurchase.price)
                if ItemToPurchase.quantity != 0:
                    item.item_quantity(ItemToPurchase.quantity)

        if num == 0:
            print()
            print('Item not found in cart. Nothing modified.')
            print()**
        
            

    def get_num_items_in_cart(self):
        total_number = 0
        items = self.cart_items[:]
        for i in range(len(items)):
            item = items[i]
            total_number += item.quantity
        return total_number

    def get_cost_of_cart(self):
        total_cost = 0
        items = self.cart_items[:]
        for i in range(len(items)):
            item = items[i]
            total_cost += (item.quantity*item.price)
        return total_cost
                       

    def print_total(self):
        print(self.customer_name + "'s Shopping Cart - " + str(self.current_date))
        count = len(self.cart_items) + 1
        if len(self.cart_items) > 0:
            print('Number of items:' + str(count))
            print()
            for i in self.cart_items:
                i.print_item_cost()
            total = self.get_cost_of_cart()
            print()
            print('Total:', str(total))
        else:
            print('SHOPPING CART IS EMPTY')

    def print_descriptions(self):
        print(self.customer_name + "'s Shopping Cart - " + str(self.current_date))
        print()
        print('Item Descriptions')
        for j in self.cart_items:
            j.print_item_description()

def print_menu(cart):
    print('MENU')
    print('a - Add item to cart')
    print('r - Remove item from cart')
    print('c - Change item quantity')
    print("i - Output items' descriptions")
    print('o - Output shopping cart')
    print('q - Quit')
    

if __name__ == "__main__":
    print("Enter customer's name:")
    customer = input()
    print("Enter today's date:")
    date = input()
    print()
    print('Customer name:', customer)
    print("Today's date:", date)
    print()
    Cart = ShoppingCart(customer, date)
    
    option = ""

    while option != 'q':
        print_menu(Cart)
        print()
        print('Choose an option:')
        option = input().lower().strip()
        if option == 'o':
            print('OUTPUT SHOPPING CART')
            Cart.print_total()
        elif option == 'i':
            print("OUTPUT ITEMS' DESCRIPTIONS")
            Cart.print_descriptions()
        elif option == 'a':
            print('ADD ITEM TO CART')
            print('Enter the item name:')
            itemName = input()
            print('Enter the item description:')
            itemDescrip = input()
            print('Enter the item price:')
            itemPrice = int(input())
            print('Enter the item quantity:')
            itemQuan = int(input())
            New_cart = ItemToPurchase()
            New_cart.name = itemName
            New_cart.quantity = itemQuan
            New_cart.price = itemPrice
            New_cart.description = itemDescrip
            Cart.add_item(New_cart)
        elif option == 'r':
            print('REMOVE ITEM FROM CART')
            print('Enter name of item to remove:')
            ItemName = input()
            Cart.remove_item(ItemName)
        elif option == 'c':
            print('CHANGE ITEM QUANTITY:')
            print('Enter the item name:')
            Item_Name = input()
            print('Enter the new quantity:')
            Item_Quantity = input()
            item_s = ItemToPurchase()
            item_s.item_quantity(Item_Quantity)
            Cart.modify_item(item_s, Item_Name)

粗体部分是 modify_item 功能。 任何帮助表示赞赏。