A function to be run after each request.

        See: http://flask.pocoo.org/docs/0.12/api/#flask.Flask.after_request

def _after_request(self, response):
        """A function to be run after each request.

        See: http://flask.pocoo.org/docs/0.12/api/#flask.Flask.after_request
        """
        # Do not trace if the url is blacklisted
        if utils.disable_tracing_url(flask.request.url, self.blacklist_paths):
            return response

        try:
            tracer = execution_context.get_opencensus_tracer()
            tracer.add_attribute_to_current_span(
                HTTP_STATUS_CODE,
                str(response.status_code))
        except Exception:  # pragma: NO COVER
            log.error('Failed to trace request', exc_info=True)
        finally:
            return response