Looping through Python command line arguments

I have a Python script that does some image manipulation and outputs a new file. From the command line, it takes two arguments, the old file and new file:

python image_converter.py oldfile.jpg newfile.jpg

I wanted to run this over a bunch of files, and used this bash script to loop over the files. This let me go over every file, and create a new file with 'new' prepended to the file name.

for f in *.jpg
python image_converter.py $f "new_$f"

I now had bunch of files, 'img1.jpg', 'img2.jpg', with their modified counterparts, 'new_img1.jpg', 'new_img2.jpg', and so on. I used this script to drop the first four characters from the new file name. Note this requires being in another directory; otherwise the new-new names just end up being the old ones.

Renaming files

for f in *.*
mv $f "${f:3}"