code: def require_app(app_name, api_style=False):
      
      iterable = (inspect.getmodule(frame[0]) for frame in inspect.stack())
      modules = [module for module in iterable if module is not None]
      if api_style:
          m = modules[2]  # skip a frame for "api" module
      else:
          m = modules[1]
      m._REQUIRED_APP = getattr(m, '_REQUIRED_APP', [])
      m._REQUIRED_APP.append(app_name)
      LOG.debug('require_app: %s is required by %s', app_name, m.__name__)
docs: Request the application to be automatically loaded.
  
      If this is used for "api" style modules, which is imported by a client
      application, set api_style=True.
  
      If this is used for client application module, set api_style=False.