def METHOD_NAME(self):
    """
    Deletes all expired cooldowns. This helps keep attribute storage
    requirements small.
    """
    now = time.time()
    cooldowns = dict(self.data)
    keys = [x for x in cooldowns.keys() if cooldowns[x] - now < 0]
    if keys:
        for key in keys:
            del cooldowns[key]
        self.obj.attributes.add(self.db_attribute, cooldowns)
        self.data = self.obj.attributes.get(self.db_attribute)