python-3.x 为什么dictionary.get()返回所有字典条目的值？

cidc1ykv 于 2023-08-08 发布在 Python

关注(0)|答案(1)|浏览(114)

下面的程序是一个使用dictionary.get（）测试print（）执行的例子。

验证码：

miles_between_oil_change = 7500
miles_warning = 500
miles_notify = miles_between_oil_change - miles_warning

def validInput(initial_mileage, final_milege):
    if initial_mileage > final_milege:
        return False
    return True

"""
Return values:
    0 - User doesn't need to change oil
    1 - User needs to change oil soon
    2 - User needs to change oil immediately
"""

def userToBeNotified(initial_mileage, final_mileage):
    miles_travelled = final_mileage - initial_mileage
    if miles_travelled < miles_notify:
        return 0
    elif miles_travelled > miles_notify:
        return 2
    else:
        return 1

def readInput():
    previous_mileage = int(input('Enter mileage of last oil change: '))
    current_milege = int(input('Enter current mileage: '))
    return previous_mileage, current_milege

def main():
    previous_mileage, current_milege = readInput()
    if not validInput(previous_mileage, current_milege):
        print('Invalid entry - Current mileage is less than mileage last changed')
        exit()

    user_notification = userToBeNotified(previous_mileage, current_milege)
    switcher = {
        0: print("User doesn't need to change oil"),
        1: print("User needs to change oil soon"),
        2: print("User needs to change oil immediately"),
    }
    switcher.get(user_notification)

if __name__ == "__main__":
    main()

字符串

输出：

Enter mileage of last oil change: 5000
Enter current mileage: 13000
User doesn't need to change oil
User needs to change oil soon
User needs to change oil immediately

型

预期输出：

Enter mileage of last oil change: 5000
Enter current mileage: 13000
User needs to change oil immediately

型
我试着调用switcher.get（），假设它只打印与键值匹配的语句。但是，我看到字典中所有条目的所有值都被打印出来了。

python-3.x

来源：https://stackoverflow.com/questions/76765371/why-is-dictionary-get-returning-values-of-all-the-dictionary-entries

1条答案

按热度按时间

ttygqcqt1#

.get()调用并不是导致打印的原因，它是在调用print的地方创建字典。如果您将代码简化为dict创建并运行它，您仍然可以看到所有三个print。尝试运行以下命令：

def main():
    switcher = {
        0: print("User doesn't need to change oil"),
        1: print("User needs to change oil soon"),
        2: print("User needs to change oil immediately"),
    }

if __name__ == "__main__":
    main()

字符串
当你写print('message')时，你会立即调用print。同样地，线

s = print('message')

型
将立即printmessage。由于print返回None，结果将是s = None。你也在做类似的事情。
您可以使用字符串本身替换print调用。然后从dict中检索字符串并打印出来

switcher = {
        0: "User doesn't need to change oil",
        1: "User needs to change oil soon",
        2: "User needs to change oil immediately",
    }
    print(switcher[user_notification])

型
如果您的意图是模拟switch语句而不是在数据中表示选项，那么您有几种选择
你可以使用和其他-如果梯子

user_notification = userToBeNotified(previous_mileage, current_milege)
    if user_notification == 0:
        print("User doesn't need to change oil")
    elif user_notification == 1:
        print("User needs to change oil soon")
    elif user_notification == 2:
        print("User needs to change oil immediately")

型
或者，如果您可以访问Python 3.10+，则可以使用match

user_notification = userToBeNotified(previous_mileage, current_milege)
    match user_notification:
        case 0:
            print("User doesn't need to change oil")
        case 1:
            print("User needs to change oil soon")
        case 2:
            print("User needs to change oil immediately")

型

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python-3.x 为什么dictionary.get()返回所有字典条目的值？

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