如何在python中创建一些空的嵌套列表
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How to create a number of empty nested lists in python
提问by Andy S. C.
I want to have a variable that is a nested list of a number of empty lists that I can fill in later. Something that looks like:
我想要一个变量，它是多个空列表的嵌套列表，我可以稍后填写。看起来像的东西：
my_variable=[[], [], [], []]
However, I do not know beforehand how many lists I will need, only at the creation step, therefore I need a variable ato determine it.
I thought about simple my_variable=[[]]*a, but that creates copies of lists and it is not what I want to have.
但是，我事先不知道我需要多少个列表，只在创建步骤中，因此我需要一个变量a来确定它。我想到了 simple my_variable=[[]]*a，但这会创建列表的副本，这不是我想要的。
I could do:
我可以：
my_variable=[]
for x in range(a):
my_variable.append([])
but I'm looking for a more elegant solution (preferably one-liner). Is there any?
但我正在寻找一种更优雅的解决方案（最好是单线）。有没有？
采纳答案by Andy S. C.
Try a list comprehension:
尝试列表理解：
lst = [[] for _ in xrange(a)]
See below:
见下文：
>>> a = 3
>>> lst = [[] for _ in xrange(a)]
>>> lst
[[], [], []]
>>> a = 10
>>> lst = [[] for _ in xrange(a)]
>>> lst
[[], [], [], [], [], [], [], [], [], []]
>>> # This is to prove that each of the lists in lst is unique
>>> lst[0].append(1)
>>> lst
[[1], [], [], [], [], [], [], [], [], []]
>>>
Note however that the above is for Python 2.x. On Python 3.x., since xrangewas removed, you will want this:
但请注意，以上内容适用于 Python 2.x。在 Python 3.x. 上，因为xrange被删除了，你会想要这个：
lst = [[] for _ in range(a)]
回答by Nullify
>>>[[] for x in range(10)] #To make a list of n different lists, do this:
[[], [], [], [], [], [], [], [], [], []]
Edit :-
编辑 ：-
[[]]*10
This will give you the same result like above but the list are not distinct instances,they are just n references to the same instance.
这将为您提供与上面相同的结果，但列表不是不同的实例，它们只是对同一实例的 n 个引用。
