How to create a list of empty lists

Question

Apologies if this has been answered before, but I couldn’t find a similar question on here.

I am pretty new to Python and what I am trying to create is as follows:

list1 = []
list2 = []
results = [list1, list2]

This code works absolutely fine, but I was wondering if there was a quicker way to do this in one line.

I tried the following, which didn’t work, but I hope it demonstrates the sort of thing that I’m after:

result = [list1[], list2[]]

Also, in terms of complexity, would having it on one line really make any difference? Or would it be three assignments in either case?

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Answer 1

If you want a one-liner you can just do:

result = [[],[]]

Answered By: dietbacon

Answer 2

For arbitrary length lists, you can use [ [] for _ in range(N) ]

Do not use [ [] ] * N, as that will result in the list containing the same list object N times

Answered By: roeland

Answer 3

results = [[],[]]

or

results = [list(), list()]

Answered By: Michael

Answer 4

For manually creating a specified number of lists, this would be good:

empty_list = [ [], [], ..... ]

In case, you want to generate a bigger number of lists, then putting it inside a for loop would be good:

empty_lists = [ [] for _ in range(n) ]

Answered By: Dawny33

Answer 5

I would suggest using numpy because you can build higher-dimensional list of lists as well:

import numpy as np
LIST = np.zeros( [2,3] )# OR np.zeros( [2,3,6] )

It works in any number of dimensions.

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