This is an app specific question: django-filter, here is a brief explanation for those who have not used it.
f = ProductFilter(request.GET, queryset=Product.objects.all())
This line does all the filtering for us. ProductFilter is a class, we have specified with filters (forms-alike class). f is a filter object (basically items we have asked for), which acts similar to a list.
Now, I'd like to perform aggregate functions (like Avg for instance) on this f object. Do you have any ideas how/if this could be accomplished?