I have a folder with lots of subfolders. Each of subfolders has different type of image files. I'm trying to rename those files by specific format. Data looks like this:

```
folder
        \ sub1\file0.jpg
        \ sub1\file1.jpg
        \ sub1\file2.png
        .
        .
        .
        \ sub2\xxx.png
        \ sub2\yyy.jpg
        \ sub2\zzz.png
        .
        .
        .

```

Desired output:

```
folder
        \ sub1\file-01.jpg
        \ sub1\file-02.jpg
        \ sub1\file-03.png
        .
        .
        .
        \ sub2\file-01.png
        \ sub2\file-02.jpg
        \ sub2\file-03.png
        .
        .
        .

```

By far, I have tried following code but it doesn't work out.

```
import os

dir_name = "D:/folder"     
for root, dirs, files in os.walk(dir_name, topdown=False):
    for file in files:
        file_name = os.path.splitext(file)[0]#file name no ext
        extension = os.path.splitext(file)[1]
        dir_name = os.path.basename(root)
        os.rename(root+"/"+file, root+"/"+"file"+"s%"+extension)

```