Python在列表理解中使用枚举

2022-01-24 00:00:00 python list list-comprehension iteration

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"]

要获得与索引一起打印的值，我可以像这样使用 Python 的 enumerate 函数

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 list comprehension 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:在列表理解中使用 enumerate 的正确方法是什么?

So, my question is: what is the correct way of using enumerate inside list comprehension?

解决方案

试试这个:

[(i, j) for i, j in enumerate(mylist)]

您需要将 i,j 放入一个元组中，列表解析才能起作用.或者，假设 enumerate() already 返回一个元组，您可以直接返回它而无需先解包:

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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