code: def filter_files_extensions(files, extension_lists):
      
      log.debug('filter_files_extensions: files="{}"'.format(files))
      result = [[] for _ in extension_lists]
      for file in files:
          ext = file.suffix[1:].lower()
          for ext_i, ext_list in enumerate(extension_lists):
              if ext in ext_list:
                  result[ext_i].append(file)
      log.debug('filter_files_extensions result:{}'.format(result))
      return result
docs: Put the files in buckets according to extension_lists
      files=[movie.avi, movie.srt], extension_lists=[[avi],[srt]] ==> [[movie.avi],[movie.srt]]
      :param files: A list of files
      :param extension_lists: A list of list of extensions
      :return: The files filtered and sorted according to extension_lists