code: def _get_user_id(arguments_dict):
      
      if 'user_id' not in arguments_dict:
          raise TypeError('Each invocation of a UserTaskMixin subclass must include the user_id')
      user_id = arguments_dict['user_id']
      try:
          get_user_model().objects.get(pk=user_id)
      except (ValueError, get_user_model().DoesNotExist):
          raise TypeError('Invalid user_id: {}'.format(user_id))
      return user_id
docs: Get and validate the `user_id` argument to a task derived from `UserTaskMixin`.
  
      Arguments:
          arguments_dict (dict): The parsed positional and keyword arguments to the task
  
      Returns
      -------
          int: The primary key of a user record (may not be an int if using a custom user model)