Renaming files with Python

I downloaded some PowerPoint slides and wmv programming videos from a college website and the original file names had spaces in them, so my browser’s downloader plugin converted the spaces to _20. I wanted to rename them so they wouldn’t have the _20 in them, and the following is the code I used to do so. Hope someone finds it useful.

import os
import os.path

files = os.listdir(os.getcwd())

for file in files:
    #if '20' and 'wmv' in file:
    if ' ' and 'ppt' in file:
        new_name = file.replace(' ', '_')
        print "%s   %s" % (file, new_name)
        os.rename(file, new_name)