code: def _retrieve_offline(data_dir, cache_key):
      logger.debug(
          "Downloading auxiliary files is turned off, will check "
          "local files."
      )
      local_file = os.path.join(data_dir, *cache_key.split("/"))
      if not os.path.isfile(local_file):
          raise RuntimeError(
              "Satpy 'download_aux' setting is False meaning "
              "no new files will be downloaded and the local "
              "file '{}' does not exist.".format(local_file)
          )
      return local_file
  
imports: import logging
  import os
  import pooch
  import satpy
label_desc: Use image node_id 3 for calling a global function with example usage: _retrieve_offline(data_dir, cache_key) and returns: local_file