code: def set_file_idx_offset(self, file_idx_offset=0):
          
          if isinstance(file_idx_offset, int):
              self.file_idx_offset = file_idx_offset
          elif file_idx_offset == 'auto':
              self.file_idx_offset = self.storage.max_file_idx()
          else:
              raise ValueError('"file_idx_offset" must be an integer or `auto`')
docs: Set offset of file index.
  
          Args:
              file_idx_offset: It can be either an integer or 'auto'. If set
                  to an integer, the filename will start from
                  ``file_idx_offset`` + 1. If set to ``'auto'``, the filename
                  will start from existing max file index plus 1.