列表理解以按元素值重复列表中的元素

问题描述

我不太清楚执行此操作的代码，有类似的帖子:重复列表理解中的元素

I can't quite figure out the code to do this, there are similar posts: Repeating elements in list comprehension

但是我想用列表中的值重复列表中的一个值

but I want to repeat a value in the list by the value in the list

In [219]:

l = [3,1]

[i for x in range(i) for i in l]
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-219-84d6f25dfd96> in <module>()
      1 l = [3,1]
      2
----> 3 [i for x in range(i) for i in l]

TypeError: 'tuple' object cannot be interpreted as an integer

我想要的是这样的列表:

What I want is a list like so:

[3,3,3,1]

也可以有人解释这个错误.

Also can someone explain the error.

请注意，我在这里运行python 3.3

Note I am running python 3.3 here

推荐答案

[x for x in l for _ in range(x)]
# Out[5]: [3, 3, 3, 1]

但是我更喜欢itertools中更详细，更直截了当的(文字)函数:

But I prefer more verbose, yet more straigforward (literal) functions from itertools:

from itertools import chain, repeat
list(chain.from_iterable(repeat(x, x) for x in l))

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