Recursive file tree add thing

Looks something like:

#!/usr/bin/env python2

import re
import os
import sys

def add_dir(dir):
filenames = os.listdir(dir)
filenames.sort()
subdirs = []
for filename in filenames:
    pathname = os.path.join(dir, filename)
    if VALID_PICTURE(filename):
        print pathname
    if os.path.isdir(pathname):
        subdirs.append(pathname)
map(add_dir, subdirs)
def VALID_PICTURE(name):
if re.search("\.(png|jpg)$", name, re.I):
    return 1
if __name__ == '__main__':
 patharg = sys.argv[1]
 print "Adding", patharg
 add_dir(patharg)