字典的KeyError

Question

我试图让用户进入一个城市，并将温度保存到字典中。但是，Python一直告诉我，我得到了一个KeyError。为什么会发生这种情况？我该如何解决这个问题？谢谢。

def main():
    city = {}
    keepgoing = True
    while keepgoing:    
        user = input("Enter city followed by temperature: ")
        for valu in user.split():
            city[valu] = city[valu]+1

        if user == "stop":
            keepgoing = False
            print(city)


main()

Answer 1

将你的for循环更改为：

city = {}
while keepgoing:
    user = input("Enter city followed by temperature: ")
    for valu in user.split():
        if valu not in city:
            city[value] = 0
        city[value] = city[value]+1

您收到错误，因为第一次valu不是city中的关键字。结果，city[valu]失败。当密钥不存在时将其设置为0（或其他一些默认值）将解决您的问题

Answer 2

要解决当前问题，请替换：

        city[valu] = city[valu]+1

使用：

        city[valu] = city.get(valu, 0) + 1

解释

city.get(valu)与city[valu]类似，只是如果密钥不存在，它会提供默认值None。 city.get(valu, 0)类似，但它将默认值设置为0。

完成计划

猜测你想要什么，这里是对代码的重写：

def main():
    city = {}
    while True:
        user = input("Enter city followed by temperature: ")
        if user == "stop":
            print(city)
            break
        name, temperature = user.split()
        city[name] = temperature

main()

在操作中：

Enter city followed by temperature: NYC 101
Enter city followed by temperature: HK 115
Enter city followed by temperature: stop
{'NYC': '101', 'HK': '115'}