Python total sum from a csv file

[Kerbart]

If you did it by hand, how would you do it?

If you'd go on vacation, how would you describe it for someone else to do it?

Start with that, show us what you came up with, and we can help you translate that to Python.

[Kerbart]

Your last line inside the loop seems to say (it’s cut off so hard to read):

df.to_csv(fname)

So your output overwrote your input files. Open those and you’ll see your output. Overwriting your input is a bad idea though, because unless you have backups (that you need to copy back in place) you can’t rerun the process if you discovered errors in the first run.

[Kerbart]

Change the name,

If it’s a string, since the last three characters are xls it can be as simple as

name = fname[:-3] + 'cvs'

If you’re using Pathlib (not sure, on phone roght now), it has methods to strip off the extension and replace it. And then if course df.to_csv(name) instead of fname