code: def close_all_files(self):
          
          while len(self.open_file_infos) > 0:
              file_info = self.open_file_infos.pop(0)
              file_info.file_handle.close()
              file_info.file_handle = None
              self.closed_file_infos.append(file_info)
          self.can_open_more_files = True
docs: Close all open files (so that we can open more).