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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def on_view_not_found( self, environ: Dict[str, Any], start_response: Callable[[str, List[Tuple[str, str]]], None], ) -> Iterable[bytes]: """ called when views not found"""

        start_response('404 Not Found', [('Content-type', 'text/plain')])
        return [b'Not found']