code: def dummy_file(self):
      if self._dummy_file is None:
          self._dummy_file = self.download_dummy_data()
      return self._dummy_file
  
imports: import os
  import re
  import urllib.parse
  from pathlib import Path
  from typing import Callable, List, Optional, Union
  from zipfile import ZipFile
  from ..utils.file_utils import cached_path, hf_github_url
  from ..utils.logging import get_logger
  from ..utils.version import Version
label_desc: Use image node_id 2 for calling the MockDownloadManager obj's underlying member method code with example usage: obj.dummy_file() and returns: self