code: def user_id(self):
          
          # This needs flask-login to be installed
          if not has_flask_login:
              return
  
          # and the actual login manager installed
          if not hasattr(current_app, 'login_manager'):
              return
  
          # fail if no current_user was attached to the request context
          try:
              is_authenticated = current_user.is_authenticated
          except AttributeError:
              return
  
          # because is_authenticated could be a callable, call it
          if callable(is_authenticated):
              is_authenticated = is_authenticated()
  
          # and fail if the user isn't authenticated
          if not is_authenticated:
              return
  
          # finally return the user id
          return current_user.get_id()
docs: Return the ID of the current request's user