如何计算subtotal的累计总和？Python总金额计算错误求助

问题根源 #

你代码里的核心问题是每次循环都重新给overall_total赋值为当前sub_total的两倍，完全没有累加之前所有采购项的金额，导致最终结果只是最后一项金额的两倍，而非总和。

修复后的代码 #

import custom

def main():
    each_item = True
    i = 0
    overall_total = 0  # 初始化总金额为0
    purchase = int(input('How many different items are being purchased? '))
    while each_item is True:
        i = i + 1
        desc = input('Enter description of item ' + str(i) + ' ')
        part = int(input('Enter part number of item ' + str(i) + ' '))
        price = int(input('Enter price of item ' + str(i) + ' '))
        quant = int(input('Enter the quantity for item ' + str(i) + ' '))
        sub_total = custom.subtotal(desc, part, price, quant)
        overall_total += sub_total  # 累加当前项的subtotal到总金额
        print(f'Item: {desc}, Part Number: {part}, subtotal: ${sub_total:.2f}\n')
        if i == purchase:
            print(f'Your total is: ${overall_total:.2f}')
            break

if __name__ == '__main__':
    main()

关键修改点 #

• 在循环开始前初始化overall_total = 0，确保总金额从0开始累加
• 把错误的overall_total = sub_total + sub_total替换为overall_total += sub_total，这行代码等价于overall_total = overall_total + sub_total，会把当前项的subtotal累加到总金额里
• 移除了未使用的total变量，精简代码

内容的提问来源于stack exchange，提问作者Tara