按字段获取queryset的不同值

我有这个模型:

class Visit(models.Model):
    timestamp  = models.DateTimeField(editable=False)
    ip_address = models.IPAddressField(editable=False)

如果用户一天内多次访问, 如何根据IP字段筛选唯一行? (我想要今天的特别访问)

today = datetime.datetime.today()
yesterday = datetime.datetime.today() - datetime.timedelta(days=1)

visits = Visit.objects.filter(timestamp__range=(yesterday, today)) #.something?

编辑:

我看到我可以使用:

Visit.objects.filter(timestamp__range=(yesterday, today)).values('ip_address')

只获取IP字段的值。现在我的查询集如下所示:

[{'ip_address': u'127.0.0.1'}, {'ip_address': u'127.0.0.1'}, {'ip_address':
 u'127.0.0.1'}, {'ip_address': u'127.0.0.1'}, {'ip_address': u'127.0.0.1'}]

如何在不评估查询集和进行db命中的情况下筛选此唯一性?

# Hope it's something like this...
values.distinct().count()