我在Python中有一个介绍性类，其中的部分说明是：
（2）使用以下数据属性和相关方法构建ShoppingCart类。注意：最初可能是一些方法存根（空方法），将在以后的步骤中完成。
add_item（）
将项目添加到cart_items列表。具有参数ItemToPurchase。不返回任何内容。
代码是：
class ItemToPurchase:
def __init__(self):
self._name = "none"
self._price = 0
self._quantity = 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 __str__(self):
print("For item " + self._name + ": " + self._description + " there are " + str(self._quantity) + " available at $" + str(self._price) + ".")
def print_item_cost(self):
print(self._name + " " + str(self._quantity) + " @ $" + str(self._price) + " = $" + str(self._quantity * self._price))
def print_item_description(self):
print(self._name + ": " + self._description)
class ShoppingCart:
def __init__(self, name="none", date="January 1, 2016"):
cart_items = []
_customer_name = name
_current_date = date
def add_item(self, cartItem):
self.cart_items.append(cartItem)
def remove_item(self, item_name):
count = 0
itms = self.cart_items[:]
for i in range(len(itms)):
itm = itms[i]
if itm._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):
count = 0
itms = self.cart_items[:]
for i in range(len(itms)):
itm = itms[i]
if itm._name == ItemToPurchase._name:
count += 1
if ItemToPurchase._description != "none":
itm.item_description(ItemToPurchase._description)
if ItemToPurchase._price != 0:
itm.item_price(ItemToPurchase._price)
if ItemToPurchase._quantity != 0:
itm.item_quantity(ItemToPurchase._quantity)
if count == 0:
print(" ")
print("Item not found in cart. Nothing modified.")
def get_num_items_in_cart(self):
count = 0
itms = self.cart_items[:]
for i in range(len(itms)):
itm = itms[i]
count += itm._quantity
return count
def get_cost_of_cart(self):
cost = 0
itms = self.cart_items[:]
for i in range(len(itms)):
itm = itms[i]
cost += (itm._quantity * itm._price)
return cost
def print_total(self):
print(self._customer_name + "'s Shopping Cart - " + self._current_date)
count = len(self.cart_items)
if count == 0:
print(" ")
print("SHOPPING CART IS EMPTY")
return 0
print("Number of Items: " + str(count))
print(" ")
for itm in self.cart_items:
itm.print_item_cost()
total = self.get_cost_of_cart()
print("Total: $" + str(total))
def print_descriptions(self):
print(self._customer_name + "'s Shopping Cart - " + self._current_date)
print(" ")
print("Item Descriptions")
for itm in self.cart_itmes:
print(itm.item_name() + ": " + itm.item_description())
def print_menu(cart):
print(" ")
print("MENU")
print("a - Add item to cart")
print("r - Remove item from cart")
print("c - Change item quntity")
print("i - Output items' descriptions")
print("o - Output shopping cart")
print("q - Quit")
print(" ")
def main():
#Define Constants and variables
custName = ""
dateToday = ""
custName = input("Enter customer's name: ")
dateToday = input("Enter today's date: ")
print("Customer name: " + custName)
print("Today's date: " + dateToday)
myCart = ShoppingCart(custName,dateToday)
option = ""
while option != "q":
print_menu(myCart)
option = input("Choose an option: ").lower().strip()
if option == "o":
myCart.print_descriptions()
elif option == "a":
print("ADD ITEM TO CART")
itemName = input("Enter the item name: ")
itemDescr = input("Enter the item description: ")
itemPrice = int(input("Enter the item price: "))
itemQuantity = int(input("Enter the item quantity: "))
print(" ")
cartItem = ItemToPurchase()
cartItem.item_name(itemName)
cartItem.item_description(itemDescr)
cartItem.item_price(itemPrice)
cartItem.item_quantity(itemQuantity)
myCart.add_item(cartItem)
elif option == "r":
print("REMOVE ITEM FROM CART")
itemName = input("Enter name of item to remove: ")
myCart.remove_item(itemName)
elif option == "c":
print("CHANGE ITEM QUNATITY")
itemName = input("Enter the item name: ")
itemQuantity = int(input("Enter the new quantity: "))
changeItem = ItemToPurchase(itemName)
changeItem.item_quantity(itemQuantity)
myCart.modify_item(changeItem)
main()
我遇到以下错误：
Enter customer's name: Rog
Enter today's date: Oct 20
Customer name: Rog
Today's date: Oct 20
MENU
a - Add item to cart
r - Remove item from cart
c - Change item quntity
i - Output items' descriptions
o - Output shopping cart
q - Quit
Choose an option: a
ADD ITEM TO CART
Enter the item name: Sketchers
Enter the item description: Black
Enter the item price: 120
Enter the item quantity: 2
回溯（最近通话最近）：文件 “ C：\ PythonWorkspace \ Chapter9Assignment \ src \ onlineShoppingCart2.py”， 176行，在 main（）文件“ C：\ PythonWorkspace \ Chapter9Assignment \ src \ onlineShoppingCart2.py”， 主线163 myCart.add_item（cartItem）文件“ C：\ PythonWorkspace \ Chapter9Assignment \ src \ onlineShoppingCart2.py”， add_item中的第44行 self.cart_items.append（cartItem）AttributeError：“ ShoppingCart”对象没有属性“ cart_items”
谁能告诉我我做错了什么？
答案 0 :(得分：1)
class ShoppingCart:
def __init__(self, name="none", date="January 1, 2016"):
cart_items = []
_customer_name = name
_current_date = date
这些都是局部变量。如果希望它们成为实例的属性，则必须显式引用self：
class ShoppingCart:
def __init__(self, name="none", date="January 1, 2016"):
self.cart_items = []
self._customer_name = name
self._current_date = date