reorder.py

import os,glob,sys
images=glob.glob(sys.argv[1])
images.sort()

if (len(images)&1) == 1:
	print("Odd number of items! Can't split")
	sys.exit(1)
midpoint = len(images)//2
first_half = images[:midpoint]
last_half = images[midpoint:][::-1]

for pagenum,(image_a, image_b) in enumerate(zip(first_half,last_half)):
	for image, suffix in ((image_a, 'a'), (image_b, 'b')):
		_,ext=os.path.splitext(image)
		os.rename(image,'renamed_{:04}{}{}'.format(pagenum,suffix,ext))