def load_file(self, filename):
        """
        load file which contains yaml configuration entries.and merge it by
        current instance

        :param files: files to load and merge into existing configuration
                      instance
        :type files: list

        """
        if not path.exists(filename):
            raise FileNotFoundError(filename)

        loaded_yaml = load_yaml(filename, self.context)
        if loaded_yaml:
            self.merge(loaded_yaml)