code: def start(check_time: int = 500) -> None:
      """Begins watching source files for changes.
  
      .. versionchanged:: 5.0
         The ``io_loop`` argument (deprecated since version 4.1) has been removed.
      """
      io_loop = ioloop.IOLoop.current()
      if io_loop in _io_loops:
          return
      _io_loops[io_loop] = True
      if len(_io_loops) > 1:
          gen_log.warning(
              "tornado.autoreload started more than once in the same process"
          )
      modify_times: Dict[str, float] = {}
      callback = functools.partial(_reload_on_update, modify_times)
      scheduler = ioloop.PeriodicCallback(callback, check_time)
      scheduler.start()
  
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 1 for calling a global function with example usage: start(check_time) without return types