<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def on_view_not_found( self, environ: Dict[str, Any], start_response: Callable) -> Iterable[bytes]: # pragma: nocover """ called when view is not found"""

        raise NotImplementedError()