Python嵌套字典理解与集合 [英] Python nested dict comprehension with sets

问题描述

有人可以解释嵌套字典的理解方式吗？

Can someone explain how to do nested dict comprehensions?

>> l = [set([1, 2, 3]), set([4, 5, 6])]
>> j = dict((a, i) for a in s for i, s in enumerate(l))
>> NameError: name 's' is not defined

我会喜欢：

>> j
>> {1:0, 2:0, 3:0, 4: 1, 5: 1, 6: 1}

我刚刚向上一个问题询问一个更简单的词汇理解，其中括号中的括号发电机功能降低。

I just asked a previous question about a simpler dict comprehension where the parentheses in the generator function were reduced. How come the s in the leftmost comprehension is not recognized?

推荐答案

在最左边的理解中， s 只是逆转两个循环的顺序：

Just reverse the order of the two loops:

j = dict((a, i) for i, s in enumerate(l) for a in s)

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