fill in missing frames in an image sequence

fill_in_sequence.py

#!/usr/bin/env python
# made for https://blender.stackexchange.com/q/112530/935
# fill in missing frames in an image sequence
# by linking missing frames to the previous existing frame

import os

base_filename = 'Display'
base_extension = '.png'
# filename is composed of basename a four digit zero padded number and extension
filename_format = '{}{:04}{}'

last_file = ''
for i in range(1,22):
    fname = filename_format.format(base_filename,i,base_extension)
    if os.path.exists(fname):
        last_file = fname
    else:
        os.symlink(last_file, fname)