def include_yaml(self, node):
        '''
        load another yaml file from the path specified by node's value
        '''
        filename = self.construct_scalar(node)
        if not filename.startswith('/'):
            if self._root is None:
                raise Exception('!include_yaml %s is a relative path, '
                                'but stream lacks path' % filename)
            filename = os.path.join(self._root, self.construct_scalar(node))
        with self.open(filename, 'r') as fin:
            return yaml.load(fin, Loader)
load another yaml file from the path specified by node's value