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python - 在哪里放置 sys.exit() 以终止代码

问题描述

这是一个初学者 Python 程序，我们在其中得到一个菜单，用户可以从 1-5 和 6 中选择要退出的项目。如果他们选择 6，它将终止代码，不问任何其他问题，也不显示账单。

我认为将它放在“elif 选择 == 6”处会起作用，但它会结束整个代码而不考虑其他先前的选择

def get_inputs():
'''get input of each of the burger choices of the user and how much did they want'''
    count = 0
    quantity1 =quantity2=quantity3=quantity4=quantity5 = 0
    flag = True
    while flag:

        check_choice = True
        while check_choice:
            try:
                choices=int(input("Enter kind of burger you want(1-5 or 6 to exit): ").strip())
                if choices <=0:
                    print("Enter a positive integer!")
                else:
                    check_choice = False
            except:
                print("Enter valid numeric value")

        check_quantity = True
        while check_quantity and choices != 6:
            try:
                quantity = int(input("Enter quantity of burgers wanted: "))
                if quantity <=0:
                    print("Enter a positive integer!")
                else:
                    count +=1
                    check_quantity = False
            except:
                print("Enter valid numeric value")
        if choices == 1:
            quantity1 = quantity
        elif choices == 2:
            quantity2 = quantity
        elif choices == 3:
            quantity3 = quantity
        elif choices == 4:
            quantity4 = quantity
        elif choices == 5:
            quantity5 = quantity
        elif choices == 6:
            flag = False

    check_staff = True
    while check_staff and count !=0:
        try:
            tax = int(input("Are you a student? (1 for yea/0 for no)"))
            check_staff = False
        except:
            print("Enter 1 or 0 only")

    return quantity1,quantity2,quantity3,quantity4,quantity5,tax

def compute_bill(quantity1,quantity2,quantity3,quantity4,quantity5,tax):
'''calculate the total amount of the burgers and the total price of the purchase'''
    total_amount = tax_amount = subtotal = 0.0
    student_tax = 0
    subtotal = (quantity1 * DA_PRICE) + (quantity2 * BC_PRICE) + (quantity3 * MS_PRICE) + (quantity4 * WB_PRICE) + (quantity5 * DCB_PRICE)

    if(tax == 0):
        tax = float(STAFF_TAX)
        tax_amount = subtotal *(tax/100)
        total_amount = subtotal + tax_amount
    elif(tax == 1):
        total_amount = subtotal+student_tax

    return tax_amount, total_amount, subtotal

预期：当启动程序并按 6 时，它会终止，不问任何其他问题，也不显示账单

预期：代码将获取用户的输入，然后当按下 6 时，它将继续执行 comput_bill 函数并计算/打印账单

实际结果：开始按6时，get_inputs中，return语句中，赋值前引用了局部变量“tax”

标签： python

解决方案

你可以只做循环，当你得到一个 6 时，你退出循环。如果没有输入，则跳过学生检查和账单计算。

这比尝试使用标志变量来检查是否应该打印要干净得多。

使用sys.exit. 是一种相当残酷的方式来终止你的程序。通常最好将终止决定委托给应用程序中的最外层函数。到达程序结束时让程序自然终止也更好。

您可能会使用sys.exit诸如不正确的命令行参数之类的东西。

# example prices.
unitprices = {
    1: 7.89,    # DA_PRICE
    2: 11.00,   # BC_PRICE
    3: 9.50,
    4: 15.85,
    5: 21.00
}

STAFF_TAX = 0.2


def calcbill(units, istaxable, unitprices=unitprices, taxrate=STAFF_TAX):

    subtotal = 0

    for u in units:
        subtotal += unitprices[u]

    if istaxable:
        tax_amount = subtotal * (taxrate / 100)
    else:
        tax_amount = 0

    return (subtotal + tax_amount, tax_amount)


entries = []

print("Enter kind of burger you want(1-5 or 6 to exit): ")

while True:
    try:
        choice = int(input("what is the next burger? "))

        if choice == 6:
            break
        elif 0 < choice < 6:
            entries.append(choice)
        else:
            print('invalid choice')
    except:
        print('not a number')

if entries:

    while True:

        s = input('Are you a student? ').lower()

        if s in ('y', 'yes', 'true'):
            isstudent = True
            break
        elif s in ('n', 'no', 'false'):
            isstudent = False
            break
        else:
            print('not a valid value')

    total, tax = calcbill(entries, not isstudent)

    print(f'the bill was ${total:.2f} which includes ${tax:.2f} tax')

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