inserting integer at each index of python list

Question

How would I insert integer '5' at each index of following list an element in new list per index

I have a list

['2', '6', '8']

and would like to insert '5' in following way:

['5', '2', '6', '8']
['2', '5', '6', '8']
['2', '6', '5', '8']
['2', '6', '8', '5']

The integer 5 or the string '5'?

khelwood
– khelwood

2020-10-20 13:15:45 +00:00
Commented Oct 20, 2020 at 13:15 — khelwood
– khelwood, Commented Oct 20, 2020 at 13:15
@schwobaseggl oh ok removing dupe.

Rakesh
– Rakesh

2020-10-20 13:26:50 +00:00
Commented Oct 20, 2020 at 13:26 — Rakesh
– Rakesh, Commented Oct 20, 2020 at 13:26

tobias_k · Accepted Answer · 2020-10-20 13:39:58Z

5

You could use a list comprehension using slices of the list to and from each index:

>>> lst = ['2', '6', '8']
>>> [lst[:i] + ["5"] + lst[i:] for i in range(len(lst)+1)]
[['5', '2', '6', '8'],
 ['2', '5', '6', '8'],
 ['2', '6', '5', '8'],
 ['2', '6', '8', '5']]

Or using *-unpacking, same result: [[*lst[:i], "5", *lst[i:]] for ...]. Both versions create a bunch of temporary list slices. The alternative would be to use a loop, make a copy of the list, and then calling insert; both approaches should have ~O(2n) per list, so it does not really make a difference.

edited Oct 20, 2020 at 13:39

answered Oct 20, 2020 at 13:34

tobias_k

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