Python замените часть в большом файле

for file in files:
    fname = os.path.join(dir, file)
    inFile = codecs.open(fname, "r", "utf-8")
    outFile = codecs.open(fname + ".new", "w", "utf-8")
    for line in inFile:
        newline = do_replacements_on(line)
        outFile.write(newline)
    inFile.close()
    outFile.close()
    os.rename(fname + ".new", fname)
Hydoza