Syntastic + Django

I just started developing on Django, and then I thought using the Syntastic syntax checker on it would be a good idea.

The problem is that it complains about some things being wrong when, in fact, they aren't.

Examples:

1. For

   from django.core.urlresolvers import reverse
   

   I get:

   error| [F0401] Unable to import 'django.core.urlresolvers'
   

2. For

   amount = self.sale_set.filter(date__year=year).aggregate(sum=Sum('amount'))["sum"]
   

   I get (where self is an Album)

   error| [E1101, Album.get_sales_total] Instance of 'Album' has no 'sale_set' member
   

This code runs perfectly even with these "errors", but how can I make Syntastic behave correctly?