Watch for change of files in directories

import os,time
path_list=['/Python Projects','/Python26',
           '/Python26/Lib','/Python26/Lib/site-packages']
path_list=[os.path.realpath(p) for p in path_list]

def files(path_list):
    fileset=set()
    for path_to_watch in path_list:
        for f in os.listdir(path_to_watch):
            fileset.add(os.path.join(path_to_watch,f))
    return fileset
    
while 'Allways':
    before=files(path_list)
    time.sleep (3)
    after=files(path_list)
    if after != before:
        added = ",".join(after-before)
        removed = ",".join(before-after)
        print 'Added: %s\nRemoved: %s\n' % (added,removed)