code: def get_file_suffix(self, path, prefix):
          
          parent = self._ensure_folder_path(path)
  
          file_list = self.drive.ListFile({
              'q': "'{}' in parents and trashed=false and title contains '{}'".format(
                  parent['id'], prefix)}).GetList()
          try:
              number_of_files = len(file_list)
          except:
              number_of_files = 0
          return '{0:04}'.format(number_of_files)
docs: Gets a valid filename