docs: def _setup_dir(self, base_dir):
          """ Creates stats directory for storing stat files.
  
              `base_dir`
                  Base directory.
              """
          stats_dir = self._sdir(base_dir)
  
          if not os.path.isdir(stats_dir):
              try:
                  os.mkdir(stats_dir)
              except OSError:
                  raise errors.DirectorySetupFail()