The cleaned up invoke prefix. i.e. mentions are ``@name`` instead of ``<@id>``.

def clean_prefix(self):
        """The cleaned up invoke prefix. i.e. mentions are ``@name`` instead of ``<@id>``."""
        user = self.context.guild.me if self.context.guild else self.context.bot.user
        # this breaks if the prefix mention is not the bot itself but I
        # consider this to be an *incredibly* strange use case. I'd rather go
        # for this common use case rather than waste performance for the
        # odd one.
        return self.context.prefix.replace(user.mention, '@' + user.display_name)