code: def load(self, filename=None):
          
          if not filename:
              filename = self.default_config_file
  
          files = self._cfgs_to_read()
          # insert last, so it will override all values,
          # which have already been set in previous files.
          files.insert(-1, filename)
  
          try:
              config = self.__read_cfg(files)
          except ReadConfigException as e:
              print(Config._format_msg('config.load("{file}") failed with {error}'.format(file=filename, error=e)))
          else:
              self._conf_values = config
  
          # notice user?
          if self.show_config_notification and not self.cfg_dir:
              print(Config._format_msg("no configuration directory set or usable."
                                        " Falling back to defaults."))
docs: load runtime configuration from given filename.
          If filename is None try to read from default file from
          default location.