docs: 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)