分配时发生Python字典键错误-我该如何解决? [英] Python dictionary key error when assigning - how do I get around this?

问题描述

我有一个这样创建的字典:

I have a dictionary that I create like this:

myDict = {}

然后我想在其中添加与另一个字典相对应的键，在其中我输入另一个值:

Then I like to add key in it that corresponds to another dictionary, in which I put another value:

myDict[2000]['hello'] = 50

所以当我将myDict[2000]['hello']传递到某个地方时，它将给出50.

So when I pass myDict[2000]['hello'] somewhere, it would give 50.

为什么Python不只是在此处创建这些条目?有什么问题我以为KeyError仅在您尝试读取不存在的条目时才会发生，但我是在这里创建它的?

Why isn't Python just creating those entries right there? What's the issue? I thought KeyError only occurs when you try to read an entry that doesn't exist, but I'm creating it right here?

推荐答案

KeyError的原因是，当您尝试访问myDict[2000]时试图读取不存在的密钥.或者，您可以使用 defaultdict :

KeyError occurs because you are trying to read a non-existant key when you try to access myDict[2000]. As an alternative, you could use defaultdict:

>>> from collections import defaultdict
>>> myDict = defaultdict(dict)
>>> myDict[2000]['hello'] = 50
>>> myDict[2000]
{'hello': 50}

defaultdict(dict)意味着，如果myDict遇到未知密钥，它将返回默认值，在这种情况下，由dict()返回的内容是空字典.

defaultdict(dict) means that if myDict encounters an unknown key, it will return a default value, in this case whatever is returned by dict() which is an empty dictionary.

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