import os.path import fnmatch import fileinput import re import string def callback(arg, directory, files): for file in files: if fnmatch.fnmatch(file,arg): for line in fileinput.input(os.path.abspath(os.path.join(directory, file)),inplace=1): if re.search('.*theunderdogs.*', line): # I changed * to .* but it would probably work without this if line = string.replace(line,'theunderdogs','the-underdogs') # old string , new string print line, os.path.walk("c:/windows/favorites", callback, "*.url") # Directory you are looking under, and file pattern