我试图编写这个小脚本来批量重命名文件扩展名。我传递了三个参数，即文件所在的目录，当前扩展名和新扩展名。

我得到的错误是

python batch_file_rename_2.py c:\craig .txt .html
Traceback (most recent call last):
  File "batch_file_rename_2.py", line 13, in <module>
  os.rename(filename, newfile) 
WindowsError: [Error 2] The system cannot find the file specified

该代码是

import os
import sys

work_dir=sys.argv[1]
old_ext=sys.argv[2]
new_ext=sys.argv[3]

files = os.listdir(work_dir)
for filename in files:
    file_ext = os.path.splitext(filename)[1]
    if old_ext == file_ext:
        newfile = filename.replace(old_ext, new_ext)
        os.rename(filename, newfile)