docs: def fetch(
              self,
              url,
              filename=None,
              decompress=False,
              force=False,
              timeout=None,
              use_wget_if_available=True):
          """
          Return the local path to the downloaded copy of a given URL.
          Don't download the file again if it's already present,
          unless `force` is True.
          """
          key = (url, decompress)
          if not force and key in self._local_paths:
              path = self._local_paths[key]
              if exists(path):
                  return path
              else:
                  del self._local_paths[key]
          path = download.fetch_file(
              url,
              filename=filename,
              decompress=decompress,
              subdir=self.subdir,
              force=force,
              timeout=timeout,
              use_wget_if_available=use_wget_if_available)
  
          self._local_paths[key] = path
          return path