code: def maybe_download(url, work_directory):
      """Download the data from Marlin's website, unless it's already here."""
      filename = url.split("/")[-1]
      filepath = os.path.join(work_directory, filename)
      if not os.path.exists(filepath):
          logger.info("Downloading to {}...".format(filepath))
          download(url, work_directory)
      return filepath
  
file_path: tensorpack/tensorpack/dataflow/dataset/caltech101.py
imports: import os
  from ...utils import logger
  from ...utils.fs import download, get_dataset_path
  from ..base import RNGDataFlow
label_desc: Use image node_id 1 for calling a global function with example usage: maybe_download(url, work_directory) and returns: filepath