rename png's numbered with an underscore

renamepng.py

import fileinput
import os.path
d = {}
for line in fileinput.input():
    s = line[:-1].split('\t')
    d[s[0]] = s[1]

for key, value in d.items():
    i = 0
    while 1:
       i += 1
       if i == 1:
           filename = '%s.png' % key
           newfilename = 'dmchanged_%s.png' % value
       else:
           filename = '%s_%i.png' % (key, i)
           newfilename = 'dmchanged_%s_%i.png' % (value, i)

       if not os.path.exists(filename): break

       os.rename(filename, newfilename)