Filtering objects inside a for loop and put into a list

So I'm trying to get the most recent Posts from the favourited tags of a certain profile and I'm having some problems with it. That's what i'm trying to do:

tags = profile.fav_tags.all()
for tag in tags:开发者_开发问答 
    s1 |= Post.objects.filter(tags__name__iexact=tag.name).distinct().order_by('-created_date')[:15]
results = chain(s1)

When i run this i get:w Exception Type: UnboundLocalError Exception Value: local variable 's1' referenced before assignment

You need to initialize your s1 variable prior to the loop, probably with empty set:

s1 = set()
for tag in tags:
    # ...