async def METHOD_NAME(self, guild: discord.Guild = None) -> List[str]:
    prefixes = []
    for p in await self.bot.get_valid_prefixes(guild):
        if self.mentionable:
            p = self.mention_re.sub(f"@{self.bot.user.name} ", p)
            if p in prefixes:
                continue
        prefixes.append(p)
    return prefixes