Metadata Preserving Audiobook Converter From .m4b -> .mp3

AudioBook.py

import os
import subprocess
import sys

cwd = os.getcwd()

files = os.listdir(cwd)

for file in files:
    extension = os.path.splitext(file)[1]
    if extension == '.m4b':
        file_name = os.path.splitext(file)[0]
        new_file_name = file_name + '.mp3'
        command = 'ffmpeg -i "' + file + '" -c copy -map_metadata 0 -c:a libmp3lame -q:a 2 "' + new_file_name + '"'
        subprocess.call(command, shell=True)
        os.remove(file)
        
sys.exit()