如何在while循环中使用try-except命令请求用户输入

Question

我是一个Python初学者，并尝试使用try ， except第一次。 我要求用户输入一个整数值，但是如果用户输入例如一个字符串，而不是结束程序，我想一次又一次地询问用户，直到给出一个整数。

此时，如果用户只给出了一个字符串，但只要他再次给出错误的输入，则该用户只被要求一次给出另一个答案，程序停止。

下面是我的意思的一个例子。

我在Stackoverflow上查看了类似的问题，但我无法解决任何建议。

travel_score = 0

while True:
    try:
        travel_score = int(input("How many times per year do you travel? Please give an integer number"))
    except ValueError:
        travel_score = int(input("This was not a valid input please try again"))


print ("User travels per year:", travel_score)

Answer 1

问题是，一旦你抛出了ValueError异常，就会在except块中捕获它，但是如果再次抛出它， except s except没有更多的东西可以捕获这些新的错误。 解决方案是仅在try块中转换答案，而不是在给出用户输入后立即转换答案。

尝试这个：

travel_score = 0
is_int = False
answer = input("How many times per year do you travel? Please give an integer number: ")

while not is_int:    
    try:
        answer = int(answer)
        is_int = True
        travel_score = answer
    except ValueError:
        answer = input("This was not a valid input please try again: ")


print ("User travels per year:", travel_score)

Answer 2

问题是您的第二个输入没有异常处理。

travel_score = 0

while True:
    try:
        travel_score = int(input("How many times per year do you travel? Please give an integer number"))
    except ValueError:
        # if an exception raised here it propagates
        travel_score = int(input("This was not a valid input please try again"))


print ("User travels per year:", travel_score)

处理此问题的最佳方法是，如果输入无效，则将信息性消息发回给用户，并允许循环返回到开头并以此方式重新提示：

# there is no need to instantiate the travel_score variable
while True:
    try:
        travel_score = int(input("How many times per year do you travel? Please give an integer number"))
    except ValueError:
        print("This was not a valid input please try again")
    else:
        break  # <-- if the user inputs a valid score, this will break the input loop

print ("User travels per year:", travel_score)

Answer 3

@Luca Bezerras答案很好，但你可以把它变得更紧凑：

travel_score = input("How many times per year do you travel? Please give an integer number: ")

while type(travel_score) is not int:    
    try:
        travel_score = int(travel_score)
    except ValueError:
        travel_score = input("This was not a valid input please try again: ")


print ("User travels per year:", travel_score)