Sort strings by the first N characters

Question

I have a text file with lines like this:

2010-02-18 11:46:46.1287 bla
2010-02-18 11:46:46.1333 foo
2010-02-18 11:46:46.1333 bar
2010-02-18 11:46:46.1467 bla
         


        

Answer 1

The built-in sort is stable, so you the effectively-equal values stay in order by default.

import operator

with open('filename', 'r') as f:
    sorted_lines = sorted(f, key=operator.itemgetter(slice(0, 24)))

At this point sorted_lines will be a list of the sorted lines. To replace the old file, make a new file, call new_file.writelines(sorted_lines), then move the new file over the old one.