code: def initialize_timetables_plugins():
      """Collect timetable classes registered by plugins."""
      global timetable_classes
  
      if timetable_classes is not None:
          return
  
      ensure_plugins_loaded()
  
      if plugins is None:
          raise AirflowPluginException("Can't load plugins.")
  
      log.debug("Initialize extra timetables plugins")
  
      timetable_classes = {
          qualname(timetable_class): timetable_class
          for plugin in plugins
          for timetable_class in plugin.timetables
      }
  
imports: from __future__ import annotations
  import importlib
  import importlib.machinery
  import importlib.util
  import inspect
  import logging
  import os
  import sys
  import types
  from pathlib import Path
  from typing import TYPE_CHECKING, Any, Iterable
  from airflow import settings
  from airflow.utils.entry_points import entry_points_with_dist
  from airflow.utils.file import find_path_from_directory
  from airflow.utils.module_loading import import_string, qualname
label_desc: Use image node_id 11 for calling a global function with example usage: initialize_timetables_plugins() without return types