Automatically generate empty lists in python [duplicate]

Question

I have no idea how to begin with this, but here's what I need. The user enters a number:

n = 3

This creates 'n' empty lists:

list_1 = []
list_2 = []
list_3 = []

That is, create 'n' number of lists, based on the input by the user.

This seems like a simple enough problem, and I am sure that I need to create a for loop, but I don't know how to go about it.

for x in range(n):
    print(list_x = [])

But this gives an obvious error:

'list_x' is an invalid keyword argument for print()

What I need is a sort of a "Create a list" function, but I don't know what it is.

I am sure there are other ways to solve my problem more elegantly, but I already have a simple solution that works, I just need to create an empty list for each step. I want to now generalize it, so that I don't have to have dozens of lists created at the beginning of the program.

Also, I am a beginner with coding, so please don't be too harsh :)

Do those lists need to be individual variables? You could generate a list of lists with as many as you need. — Mikael
– Mikael, Commented Sep 23, 2020 at 13:55
If you have multiple things indexed by a number, think list. If indexed by something else, think dict. — Mad Physicist
– Mad Physicist, Commented Sep 23, 2020 at 13:57
@Mikael I am not sure if I understand you, but each list needs to be able to hold different elements... — Vikrant Srivastava
– Vikrant Srivastava, Commented Sep 24, 2020 at 6:57

solid.py · Accepted Answer · 2020-09-23 13:57:17Z

1

You could make a dictionary, where each key is the name of the list, and each value contains an empty list.

n = 3
dic = {f'list{i}': [] for i in range(1, n+1)}
print(dic)

Output:

{'list1': [], 'list2': [], 'list3': []}

answered Sep 23, 2020 at 13:57

solid.py

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4 Comments

Mad Physicist Over a year ago

What about a list of lists?

solid.py Over a year ago

@MadPhysicist Sure thing, but this approach keeps the naming conventions of lists e.g list_1, list_2, list_3. I was about to edit a default dict approach

Vikrant Srivastava Over a year ago

This indeed created a list. But how do I access the list (I need to append to it)? I tried to use "list1", and I got an error saying "list1 is not defined"

solid.py Over a year ago

@VikrantSrivastava Good question. Type it dic['list1']. Mind the quotes. The keys are strings therefore it's 'list1' not list1 (without quotes).

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