Writes all files that end with a certain extentsion to a .txt file

list.py

import os

# Writes all files that end with a certain extentsion to a .txt file
# Works in both Python 2 and Python 3
extension = ".png"
fileList = os.listdir('Outflow-Icons')
for fichier in fileList[:]: # filelist[:] makes a copy of filelist.
    if not(fichier.endswith(extension)):
        fileList.remove(fichier)

textFile = open("output.txt", "w")
for item in fileList:
    textFile.write('"{}",\n'.format(item))