docs: def _assert_dirs_exist(self, setting_name):
          """Check that the dirs leading up to the given file path exist.
  
          Does not check if the file exists.
  
          """
          v = self._get_setting(setting_name)
          if (not os.path.isdir(os.path.split(v)[0])) or os.path.isdir(v):
              self.raise_config_error(
                  setting_name,
                  v,
                  str,
                  'a file path in an existing directory',
                  is_none_allowed=False,
              )