具有多个 IF 条件的 While 循环

Question

我编写了一个程序，它从用户那里接收一个代表购物清单的字符串。 程序要求用户输入一个介于 1 和 9 之间的数字。根据收到的数字，执行以下操作之一： 在做出用户选择后，用户返回主菜单，直到他们 select 数字 9 退出。 语法是正确的，但程序没有打印出需要的内容。 如何解决？

def shopping_list(my_str):
    my_list = my_str.split(",")
    i = input("Please choose a number between 1 and 9: ")
    while i in range(1, 10):
        if i == 1:
            print("My shopping list:", my_list)
            continue
        elif i == 2:
            print("The number of items in my shopping list:", len(my_list))
            continue
        elif i == 3:
            product = input("Please enter a product name: ")
            if product in my_list:
                print("This product is in the shopping list.")
            else:
                print("This item is not in the shopping list.")
            continue
        elif i == 4:
            product = input("Please enter a product name: ")
            print("The item", product, "shows", my_list.count(product), "in the list")
            continue
        elif i == 5:
            product = input("Please enter a product name: ")
            new_list = my_list.remove(product)
            print("The item", product, "remove from the list. The new list is", new_list)
            continue
        elif i == 6:
            product = input("Please enter a product name: ")
            my_list += product
            print("The item", product, " add to the list. The new list is", my_list)
            continue
        elif i == 7:
            new_list = []
            for product in my_list:
                if len(product) < 3 or not(product.isalpha()):
                    new_list += product
            continue
        elif i == 8:
            print(list(set(my_list)))
            continue
        else:
            break
shopping_list("Milk,Cottage,Tomatoes")

Answer 1

• 您永远不会再次询问用户，因此循环会无限执行用户给出的第一选择。
• 还要删除continue语句，你不需要它们，因为所有代码都在elif中，它还允许你在循环结束时询问用户一个新的选择。
• 将输入转换为int ，您将无法进入循环

def shopping_list(my_str):
    my_list = my_str.split(",")
    i = int(input("Please choose a number between 1 and 9: "))
    while i in range(1, 10):
        if i == 1:
            print("My shopping list:", my_list)                
        elif i == 2:
            print("The number of items in my shopping list:", len(my_list))
        elif i == 3:
        # ...
        elif i == 8:
            print(list(set(my_list)))
        else:
            break
        i = int(input("Please choose a number between 1 and 9: "))

最终完整代码

---

现在更正关于

• mode 5 ： remove返回的是None ，修改是in-place so do

   elif i == 5: product = input("Please enter a product name: ") my_list.remove(product) print("The item", product, "remove from the list. The new list is", my_list)

• mode 6运算符+=对列表进行extend ，因此它将添加所有字符，而不是append

   elif i == 6: product = input("Please enter a product name: ") my_list.append(product) print("The item", product, " add to the list. The new list is", my_list)

• mode 7如果您忘记它，创建一个作为主列表过滤器的新列表是无用的。 另外我想说你删除小于 3 或包含非 alpha 的项目，在这里你保留它们。 最后使用append

   elif i == 7: new_list = [] for product in my_list: if len(product) >= 3 and product.isalpha(): new_list.append(product) my_list = list(new_list)

  或者只使用列表理解

  elif i == 7: my_list = [p for p in my_list if len(p) >= 3 and p.isalpha()]

Answer 2

我会这样做：（由于代码太多，删掉一些 elifs。）

while True:
    i = int(input("Please choose a number between 1 and 9: "))

    if i == 1:
            print("My shopping list:", my_list)
            continue
        elif i == 8:
            print(list(set(my_list)))
            continue
        elif i == 9:
            break
        else:
            print("Invalid Number! Try again.")

这是你想要的吗？ 我不太明白你的要求。