How to use the falcon.HTTP_404 function in falcon

def test_clusters_listing_with_no_etcd_result(self):
        """
        Verify listing Clusters handles no etcd result properly.
        """
        with mock.patch('cherrypy.engine.publish') as _publish:
            _publish.return_value = [[[], etcd.EtcdKeyNotFound()]]

            body = self.simulate_request('/api/v0/clusters')
            self.assertEqual(self.srmock.status, falcon.HTTP_404)
            self.assertEqual('{}', body[0])

def on_head(self, req, resp, project_id, queue_name):
        if self._queue_controller.exists(queue_name, project=project_id):
            resp.status = falcon.HTTP_204
        else:
            resp.status = falcon.HTTP_404

        resp.content_location = req.path

def on_get(self, req, resp, session_id):
        # GET /v1/sessions/{session_id}     retrieves the specified session
        # search in body
        user_id = req.get_header('X-User-ID') or ''
        obj = self.db.get_session(user_id=user_id, session_id=session_id)
        if obj:
            resp.body = obj
        else:
            resp.status = falcon.HTTP_404

}

ERR_DATABASE_ROLLBACK = {
    'status': falcon.HTTP_500,
    'code': 77,
    'title': 'Database Rollback Error'
}

ERR_DATABASE_CONNECTION = {
    'status': falcon.HTTP_500,
    'code': 76,
    'title': 'Database Connection Error'
}

ERR_NOT_SUPPORTED = {
    'status': falcon.HTTP_404,
    'code': 10,
    'title': 'Not Supported'
}

ERR_USER_NOT_EXISTS = {
    'status': falcon.HTTP_404,
    'code': 21,
    'title': 'User Not Exists'
}

ERR_USER_ALREADY_EXISTS = {
    'status': falcon.HTTP_400,
    'code': 25,
    'message': 'Users Already Exists'
}

def on_get(self, request, response, user_id=None):
        """Responds to GET request for users."""
        if user_id == self.config['relay_uid']:
            response.status = falcon.HTTP_200
            response.body = json.dumps({})
            self.api.as_register(user_id, self.config['as_token'])
        else:
            response.status = falcon.HTTP_404
            response.body = json.dumps({})

def process_response(self, req, resp, resource=''):

        """Intercept main 404 response by Falcon

        If the API hits a non existing endpoint, it will trigger a customized
        404 response that will redirect people to the documentation.

        Raises:
            HTTP 404: A falcon.HTTP_404 error

        Returns:
            JSON: A customized JSON response
        """
        if resp.status == falcon.HTTP_404:
            resp.body = json.dumps({"message": "Resource not found",
                                    "documentation": settings.__docs__})

def _producer_not_found():
    """
    sends an http 404 response to the caller
    """
    api.abort(falcon.HTTP_404, 'Unable to locate event producer.')

def on_get(self, req, resp, site_name=None):
        if site_name is None:
            site_name = 'bizocean'
        elif not self.site_exists(site_name, "swallow"):
            resp.status = falcon.HTTP_404
            message = 'site name not found:{0}'.format(site_name)
            resp.body = message
            self.logger.error(message)
            return

        resp.set_header('Access-Control-Allow-Origin', '*')

        """
        item_dict = { key: (
                            user_data,
                            validate_schema
                            ),
                    }
        key is BigQuery's column name
        """

elif filetype == 'html':
            resp.content_type = 'text/html'
        elif filetype == 'css':
            resp.content_type = 'text/css'
        else:
            resp.content_type = 'text/plain'
        resp.set_header('Access-Control-Allow-Origin', '*')
        name = os.path.normpath(name)
        filetype = os.path.normpath(filetype)
        file_path = os.path.join('static', filetype, name)
        try:
            with open(file_path, 'r', encoding='utf8') as f:
                raw_body = f.read()
        except Exception as e:
            resp.body = "{0} {1}".format(e, name)
            resp.status = falcon.HTTP_404
            return
        else:
            resp.body = raw_body.replace('{%oceanus_host%}',
                                         OCEANUS_SWALLOW_HOST)

def on_post(self, req, resp, site_name):
        if not self.site_exists(site_name, "pirate"):
            resp.status = falcon.HTTP_404
            message = 'site name not found:{0}'.format(site_name)
            resp.body = message
            self.logger.error(message)
            return
        self.logger.debug("{}".format(req.query_string))
        resp.set_header('Access-Control-Allow-Origin', '*')
        """
        item_dict = { key: (
                            user_data,
                            validate_schema
                           ),
                    }
        key is BigQuery's column name
        """
        item_dict = {
            'dt':  (