在终端上清洁地处理用户输入而不会崩溃

Question

我有这个简单的项目要做.这是我到目前为止的代码,它工作得非常好.但如果有人输入字母或未知符号,程序会崩溃.如果输入错误的内容,如何进行此错误验证并显示或打印消息？

def excercise5():

    print("Programming Excercise 5")
    print("This program calculates the cost of an order.")
    pound = eval(input("Enter the weight in pounds: "))
    shippingCost = (0.86 * pound) + 1.50
    coffee = (10.50 * pound) + shippingCost
    if pound == 1:
        print(pound,"pound of coffee costs $", coffee)
    else:
        print(pound,"pounds of coffee costs $", coffee)
    print()

excercise5()

Answer 1

我建议不要使用eval.从安全角度来看,它并不好.只需显式转换为所需类型:

pound = float(input("Enter the weight in pounds: "))

要处理无效输入:

try:
    pound = float(input("Enter the weight in pounds: "))
except ValueError:
    print('Invalid input.')
    return
# the rest of the code

要么:

try:
    pound = float(input("Enter the weight in pounds: "))
except ValueError:
    print('Invalid input.')
else:
    # the rest of the code

您还可以将输入包装在无限循环中,该循环将在成功转换时终止:

while True:
    try:
        pound = float(input("Enter the weight in pounds: "))
    except ValueError:
        print('Invalid input. Try again.')
    else:
        break
# do the rest with `pound`