python - 在 Python 3 中尝试除外

Question

我为此苦苦思索了几个小时，终于弄清楚了。当然，现在对我来说这似乎是显而易见的痛苦，但也许有一天其他人也会陷入同样的​​境地，所以我想我应该问并回答。当然，欢迎任何更正或解释。

精简代码:

bearNames = {
    'grizzly' : 'GZ',
    'brown' : 'BR',
}

bearAttributes = {
    'GZ' : 'huge and light brown',
    'BR' : 'medium and dark brown',
}

print("Type the name of a bear:")
userBear = input("Bear: ")

beartruth = True
while beartruth == True:

    try:
        print("Abbreviation is ", bearNames[userBear])
        print("Attributes are ", bearAttributes[bearNames[userBear]])
        print("beartruth: ", beartruth)
        beartruth = False
        print("beartruth: ", beartruth)

    except:
        print("Something went wrong - did you not type a bear name?")
        print("beartruth: ", beartruth)

问题 - 输入不是熊的东西会永远循环“异常(exception)”部分。我想要发生的事情应该是相当明显的 - 如果用户输入的内容不在 bearNames 中，它应该触发 except，打印错误并返回尝试。

Answer 1

因为您要求一些更正或解释。

来自您的代码

try:
    print("Abbreviation is ", bearNames[userBear])
    print("Attributes are ", bearAttributes[bearNames[userBear]])
    print("beartruth: ", beartruth)
    beartruth = False
    print("beartruth: ", beartruth)

except:
    print("Something went wrong - did you not type a bear name?")
    print("beartruth: ", beartruth)

您可以具体说明(我建议这样做)异常，以确保隔离您可能期望的错误。

try:
    print("Abbreviation is ", bearNames[userBear])
except KeyError:
    print("Something went wrong - did you not type a bear name?")
    print("beartruth: ", beartruth)
else:
    print("Attributes are ", bearAttributes[bearNames[userBear]])
    print("beartruth: ", beartruth)
    beartruth = False
    print("beartruth: ", beartruth)

这样做，你就知道熊实际上不是一只。仅当熊是真实的熊时，您才可以进入else block 执行其他操作。

如果您在最后 4 行中犯了错误，则引发的异常将有所不同，并且不会被泛型隐藏

except:

阻止，这也会隐藏其他错误，但您会认为这是用户的错误输入。

因为您处于 while 循环中，所以您也可以执行以下操作:

try:
    print("Abbreviation is ", bearNames[userBear])
except KeyError:
    print("Something went wrong - did you not type a bear name?")
    print("beartruth: ", beartruth)
    continue  # go back to the beginning of the loop

# There was no error and continue wasn't hit, the Bear is a bear
print("Attributes are ", bearAttributes[bearNames[userBear]])
print("beartruth: ", beartruth)
beartruth = False
print("beartruth: ", beartruth)