Question

我正在尝试打印购物清单的总数，但每次调用字符串时都会打印0而不是它应该是什么。

cash_due = 0
import pickle
picklee = open('Store_stuff.pickle', 'rb')
contents = pickle.load(picklee)
picklee.close()


shopping_list = ['Name      price       quantity        total']

store_contents ='''Store Contents

Name        Price       GTIN-8 Code
Butter      £1.20       70925647
Chocolate   £1.00       11826975
Bread       £1.00       59217367
Cheese      £2.80       98512508
Bacon       £2.40       92647640
Lamb        £4.80       49811230
Ham         £2.59       53261496
Potatoes    £2.00       11356288
Chicken     £3.40       89847268
Eggs        £1.29       21271243'''

def item(barcode, quantity, cash_due, shopping_list):
    shopping_list.append(contents[barcode]['name']+'      £'+(str((int(contents[barcode]['price']))/100))+'           '+str(quantity)+'            £'+str((int(quantity)*int(contents[barcode]['price']))/100))
    print(cash_due)
    print(contents[barcode]['price'])
    print(quantity)
    cash_due += ((int(contents[barcode]['price'])*(int(quantity)))/100)
    print(cash_due)

def shopkeeper_ui():
    print('Welcome to Stanmore\'s Food Emporium! Feel free to browse.')
    print(store_contents)
    user_input = ''

    while user_input != 'finish':
        user_input = input('''Welcome to the checkout.
instructions -
if you are entering text make sure your \'CAP\'s Lock\' is turned off
if you are entering a barcode number, please enter it carefully
if you want to print your current recipt, enter \'recipt\'
if you want to see your current total, enter \'total\'
and if you are finished, enter \'finish\'

You can see the stores contents below
Thanks for shopping:  ''')

        if len(user_input) == 8:
            quantity = int(input('Enter the quantity that you want:  '))
            item(user_input, quantity, cash_due, shopping_list)
        elif user_input == 'recipt':
            count8 = 0
            for i in shopping_list:
                print(shopping_list[count8])
                count8 += 1
        elif user_input == 'finish':
            print('Your shopping list is',shopping_list,' \nand your total was', total,'\n Thank you for shopping with Stanmore\'s Food Emporium')
        elif user_input == 'total':
            print('your total is, £',cash_due)
        else:
            print('User_input not valid. Try again...')
shopkeeper_ui()

如果我输入代码，我的第一个条目是21271243（鸡蛋的条形码）。然后我为数量输入4。我可以让shopping_list list了解总数，如果我从项目函数中打印字符串cash_due它理解它，但是当我尝试从shopkeeper_ui函数调用cash_due时它会打印0而不是什么应该是5.12？

Answer 1

cash_due is not mutable。离开函数时，item函数的更改将丢失。

通常，解决方法是让函数（item）返回值。

在这种情况下，我只会将cash_due保留在item函数之外，让item仅返回该项目的费用。像这样：

def item(barcode, quantity, shopping_list):
    shopping_list.append(contents[barcode]['name']+'      £'+(str((int(contents[barcode]['price']))/100))+'           '+str(quantity)+'            £'+str((int(quantity)*int(contents[barcode]['price']))/100))
    print(contents[barcode]['price'])
    print(quantity)
    cost = ((int(contents[barcode]['price'])*(int(quantity)))/100)
    print(cost)
    return cost

[...]

       if len(user_input) == 8:
            quantity = int(input('Enter the quantity that you want:  '))
            cash_due += item(user_input, quantity, shopping_list)

您对shopping_list没有相同的问题，因为它是可变的：它已在适当的位置更改。阅读有关mutables以了解这个概念。

然而，不让项目修改列表可能是更好的设计。它可以只返回列表元素和成本，调用者将修改列表。

def item(barcode, quantity):
    stuff = (contents[barcode]['name']+'      £'+(str((int(contents[barcode]['price']))/100))+'           '+str(quantity)+'            £'+str((int(quantity)*int(contents[barcode]['price']))/100))
    cost = ((int(contents[barcode]['price'])*(int(quantity)))/100)
    return stuff, cost

[...]

       if len(user_input) == 8:
            quantity = int(input('Enter the quantity that you want:  '))
            stuff, cost = item(user_input, quantity, shopping_list)
            shopping_list.append(stuff)
            cash_due += cost

str没有被要求时重置为0？

1 个答案: