How to edit a line in middle of txt file without overwriting everything?

Question

I have written a python script which read from a txt file and perform basic tasks like adding new line, deleting and editing existing lines. For deleting and editing, I load whole file as a list using "readlines()" and then overwrite file using edited list. This increases chance of data loss. So my question is, if I can edit txt files without overwriting them?

Answer 1

The traditional solution is to copy the original file to a .sav file and then write the new edited version to the original filename:

>>> import os
>>> filename = 'somefile.txt'
>>> with open(filename) as f:
        lines = f.readlines()
>>> basename, ext = os.path.splitext(filename)
>>> savefile = basename + '.sav'
>>> os.rename(filename, savefile)
>>> lines = map(str.upper, lines)    # do your edits here
>>> with open(filename, 'w') as f:
        f.writelines(lines)