Find files in amo2009 to delete

import re
import os
import shlex
import subprocess as sub
import stat


def walktree (top = ".", depthfirst = True):
    names = os.listdir(top)
    if not depthfirst:
        yield top, names
    for name in names:
        try:
            st = os.lstat(os.path.join(top, name))
        except os.error:
            continue
        if stat.S_ISDIR(st.st_mode):
            for (newtop, children) in walktree (os.path.join(top, name), depthfirst):
                yield newtop, children
    if depthfirst:
        yield top, names

if __name__ == '__main__':
    # ack for all the references to amo2009 images
    p = sub.Popen(["ack", "amo2009", "media"], stdout=sub.PIPE,stderr=sub.PIPE)
    output_media, errors = p.communicate()



    p = sub.Popen(["ack", "amo2009", "apps"], stdout=sub.PIPE,stderr=sub.PIPE)
    output_app, errors = p.communicate()

    all_files = output_media + output_app

    files_used = set(re.findall("amo2009/(.*?.(?:png|jpg|gif))", all_files))

    files_delete = []
    files_exist = []

    print "FILES TO DELETE:"

    for (basepath, children) in walktree("media/img/amo2009/",False):
        for child in children:
            filename = os.path.join('/'.join(basepath.split('/')[3:]), child)
            if not filename.startswith(".git") and filename.rfind(".") > 0:
                files_exist.append(filename)
                if not filename in files_used:
                    files_delete.append(filename)
                    print "  - %s" % filename

    print "BUT WAIT! DON'T FORGET ABOUT:"
    for filename in set(files_used) - set(files_exist):
        print '  - %s' % filename