middleware to capture doesnot exists exception

class CheckDoesNotExistsMiddleware(object):

    def process_exception(self, request, exception):
        if isinstance(exception, ObjectDoesNotExist):
            raise Http404

in settings.py 
MIDDLEWARE_CLASSES = (
    ...........
    ...........
    'gcrmserver.apps.core.middleware.CheckDoesNotExistsMiddleware',

)