Python字典理解给出了KeyError [英] Python dictionary comprehension gives KeyError
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问题描述
>>> a = 1
>>> print { key: locals()[key] for key in ["a"] }
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 1, in <dictcomp>
KeyError: 'a'
如何用这样的理解创建一个字典？
How can I create a dictionary with a comprehension like this?
推荐答案
一个dict的理解有其自己的命名空间和 locals（） 在该命名空间中没有 a 。从技术上讲，除了最外层迭代（这里 [a] ）的初始迭代之外的所有内容都几乎作为嵌套函数运行，最外层的iterable作为参数传入。
A dict comprehension has its own namespace, and locals() in that namespace has no a. Technically speaking, everything but the initial iterable for the outermost iterable (here ["a"]) is run almost as a nested function with the outermost iterable passed in as an argument.
如果您使用 globals（），或者创建了对
Your code works if you used globals() instead, or created a reference to the locals() dictionary outside of the dict comprehension:
l = locals()
print { key: l[key] for key in ["a"] }
演示：
>>> a = 1
>>> l = locals()
>>> { key: l[key] for key in ["a"] }
{'a': 1}
>>> { key: globals()[key] for key in ["a"] }
{'a': 1}
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