python to run command when something changes in directory

check_changes.py

#THANKS TO: http://timgolden.me.uk/python/win32_how_do_i/watch_directory_for_changes.html

#time for pooling in seconds
TIME = 2 
#path to watch this version don't recursive
PATH = "." 
#command to execute when something changes
COMMAND = "dir" 

import os, time
before = dict ([(f, os.stat(f).st_mtime) for f in os.listdir (PATH)])
while 1:
  time.sleep (TIME)
  after = dict ([(f, os.stat(f).st_mtime) for f in os.listdir (PATH)])
  modified = [f for f in before.keys() if not before.get(f, None) == after.get(f, None)]
  if modified:
    os.system(COMMAND)
  before = after

TODO: make it recursive