code: def register_file_change_callback(
      self, cb: Callable[[str], None]
  ) -> None:
      self._on_file_changed.append(cb)
  
imports: import collections
  import os
  import sys
  import types
  from typing import Callable, Dict, List, Optional, Set
  from streamlit import config, file_util
  from streamlit.folder_black_list import FolderBlackList
  from streamlit.logger import get_logger
  from streamlit.source_util import get_pages
  from streamlit.watcher.path_watcher import NoOpPathWatcher, get_default_path_watcher_class
label_desc: Use image node_id 3 for calling the LocalSourcesWatcher obj's underlying member method code with example usage: obj.register_file_change_callback(cb) without return types