How to reading .txt file and rewriting by adding space after specific position / index for each line in python

Question

I want to read .txt file and add space after a specific position/index for each line. please consider below example for more details.

suppose my file contains

Answer 1

Here is another solution using generator expressions.

If you are happy to provide the list of indices after each space rather than before, this will do the job:

line = '12345 678 91011 12 1314'
idx = [3, 7, 12, 22]
' '.join([line[i:j] for i, j in zip([None]+idx, idx+[None])])

which gives '123 45 6 78 91 011 12 131 4'.

Otherwise you would need to first add one to each index:

idx = [2, 6, 11, 21]
idx = [i+1 for i in idx]