Appending a value to a list of lists

Question

Here is a mock-example of what I'm trying to achieve:

I have initially a list of empty lists of size 5:

l = [[] for _ in range(5)]

Then, in a for loop that does 4 iterations, I have function that returns a list of indexes. I'd like to append "t" to the lists with those indexes.

Something like:

for t in range(4):
    idx = function_that_gives_indexes()
    l[idx].append(t)

Let's say that function_that_gives_indexes() , gives for each loop these value: [1], [2, 4], [] and [0, 1] . I'd like l to be:

l = [[3], [0, 3], [1], [], [1]]

What's the most pythonic way of doing this?

Answer 1

Since your function returns a list each time then your corrected code snippet is something like

for t in range(4):
    for idx in function_that_gives_indexes():
        l[idx].append(t)

And it does not look promising to try to make it more pythonic.