>>284
なんかいろいろまちがっててよくわからんけど
こうしたかったんじゃないか？

# -*- coding: utf-8 -*-

import os

targetpath = r"C:\test"

filelist = os.listdir(targetpath)

for filename in filelist:
    print filename

c = 1
for filename in filelist:
    oldpath = os.path.join(targetpath, filename)
    newpath = os.path.join(targetpath, '%03d.mp3' % c)
    os.rename(oldpath, newpath)
    c += 1