'Returns a copy of `stat` with `self.name` prepended to `stat.name`.'

def _prepend_name(self, stat):

    if (not isinstance(stat, statistics.Statistic)):
        raise InvalidStatisticsException(('Expecting    Statistic    object,    got    %s' % stat))
    stat_copy = stat.copy()
    stat_copy.name = ((self._name + '_') + stat_copy.name)
    return stat_copy
