Python resize image keeping aspect ratio

This time I am posting just a little snippet which came in handy with the latest web development I am doing. The problem was to resize an uploaded image on the fly and creating an according thumbnail for that image. For testing purposes I create a script that could be executed on a number of files. So here it is

import os, sys, Image

size = 150, 150

for input in sys.argv[1:]:
    output = os.path.splitext(input)[0] + ".thumbnail"
    if input != output:
        try:
            im = Image.open(input)
            im.thumbnail(size, Image.ANTIALIAS)
            im.save(output, 'JPEG')
        except IOError:
            print "Could not create thumbnail for %s" % input

python resize.py /path/to/files/*

Hope this helps anybody coming across the same problem. Quick and dirty :)