In Python 3:

Open a python file and write to a new file with line numbers and a file extension of .txt. So if you read in a file that contains:

Two roads diverged in a yellow wood, And sorry I could not travel both And be one traveler, long I stood And looked down one as far as I could To where it bent in the undergrowth

It would be saved to a second file as:

1. Two roads diverged in a yellow wood, 2. And sorry I could not travel both 3. And be one traveler, long I stood 4. And looked down one as far as I could 5. To where it bent in the undergrowth

Use any numbering look you want, for example: 1) 2) or #1 #2 or another look of your choice.