code: def watch(filename: str) -> None:
      """Add a file to the watch list.
  
      All imported modules are watched by default.
      """
      _watched_files.add(filename)
  
imports: import os
  import sys
  import functools
  import importlib.abc
  import os
  import pkgutil
  import sys
  import traceback
  import types
  import subprocess
  import weakref
  from tornado import ioloop
  from tornado.log import gen_log
  from tornado import process
  from typing import Callable, Dict, Optional, List, Union
label_desc: Use image node_id 3 for calling a global function with example usage: watch(filename) without return types