docs: def call_user_func(settings_module, func_name, *args, **kwargs):
      """Call a user-supplied settings function and clean it up afterwards.
  
      settings_module may be None, or the function may not exist.
      If the function exists, it is called with the specified *args and **kwargs,
      and the result is returned.
      """
      if settings_module:
          if hasattr(settings_module, func_name):
              func = getattr(settings_module, func_name)
              try:
                  return func(*args, **kwargs)
              finally:
                  # cleanup user function
                  delattr(settings_module, func_name)