code: def parser_add(self, parser, prefix=''):
          
          if prefix:
              prefix += '.'
          for key, value in self.items():
              value.parser_add(parser, prefix + key)
docs: Add config to an :py:class:`argparse.ArgumentParser` object.
  
          The parser’s :py:meth:`~argparse.ArgumentParser.add_argument`
          method is called for each config item. The argument name is
          constructed from the parent and item names, with a dot
          separator.
  
          :param argparse.ArgumentParser parser: The argument parser object.
  
          :keyword str prefix: The parent node name.