Python使用枚举里面的列表理解 [英] Python using enumerate inside list comprehension
问题描述
假设我有一个这样的列表:
Lets suppose I have a list like this:
mylist = ["a","b","c","d"]
要获得打印的值及其索引,我可以使用Python的枚举
这样的功能
To get the values printed along with their index I can use Python's enumerate
function like this
>>> for i,j in enumerate(mylist):
... print i,j
...
0 a
1 b
2 c
3 d
>>>
现在,当我尝试在列表理解中使用它时
它给了我这个错误
Now, when I try to use it inside a list comprehension
it gives me this error
>>> [i,j for i,j in enumerate(mylist)]
File "<stdin>", line 1
[i,j for i,j in enumerate(mylist)]
^
SyntaxError: invalid syntax
所以,我的问题是:什么是正确的方法使用枚举内部列表理解?
So, my question is: what is the correct way of using enumerate inside list comprehension?
推荐答案
试试这个:
[(i, j) for i, j in enumerate(mylist)]
你需要在元组中放入 i,j
才能使列表理解起作用。或者,假设 enumerate()
已经返回一个元组,你可以直接返回它而不首先解压缩它:
You need to put i,j
inside a tuple for the list comprehension to work. Alternatively, given that enumerate()
already returns a tuple, you can return it directly without unpacking it first:
[pair for pair in enumerate(mylist)]
无论哪种方式,返回的结果都符合预期:
Either way, the result that gets returned is as expected:
> [(0, 'a'), (1, 'b'), (2, 'c'), (3, 'd')]
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