double for loops in python

Try this:

for md in range(1,5):
   for pico in range(21,25):
      print "file-{0}-loop-{1}".format(md, pico)

Or:

from itertools import product
for md, pico in product(range(1,5), range(21,25)):
    print "file-{0}-loop-{1}".format(md, pico)