def METHOD_NAME(self, stat, formatter=None):
    """Add a stat to the list.
    :param StatBase stat:
    :param Union[None,StatFormatter] formatter:
    """
    assert isinstance(stat, statsmdl.StatBase)
    self.stats.METHOD_NAME(stat)
    _formatter = formatter
    if type(_formatter) is str:
        _formatter = StatFormatter(formatter=_formatter)
    self.formatters[stat.name] = _formatter