  
      def test_foreignkey(self):
          with self.assertNumQueries(2):
              qs = AuthorWithAge.objects.prefetch_related('addresses')
              addresses = [[six.text_type(address) for address in obj.addresses.all()] for obj in qs]
          self.assertEqual(addresses, [[six.text_type(self.author_address)], [], []])
  
      def test_foreignkey_to_inherited(self):
          with self.assertNumQueries(2):
              qs = BookReview.objects.prefetch_related('book')
              titles = [obj.book.title for obj in qs]
 
</s> remove             addresses = [[six.text_type(address) for address in obj.addresses.all()]
 </s> add             addresses = [[str(address) for address in obj.addresses.all()] </s> remove         self.assertEqual(addresses, [[six.text_type(self.author_address)], [], []])
 </s> add         self.assertEqual(addresses, [[str(self.author_address)], [], []]) </s> remove         lst2 = [[six.text_type(book) for book in author.books_with_year.all()] for author in qs]
 </s> add         lst2 = [[str(book) for book in author.books_with_year.all()] for author in qs] </s> remove         lst2 = [[six.text_type(author) for author in book.aged_authors.all()] for book in qs]
 </s> add         lst2 = [[str(author) for author in book.aged_authors.all()] for book in qs] </s> remove             lst = [[six.text_type(book) for book in author.books_with_year.all()] for author in qs]
 </s> add             lst = [[str(book) for book in author.books_with_year.all()] for author in qs]
            addresses = [[str(address) for address in obj.addresses.all()] for obj in qs]
        self.assertEqual(addresses, [[str(self.author_address)], [], []])
  
      def test_foreignkey(self):
          with self.assertNumQueries(2):
              qs = AuthorWithAge.objects.prefetch_related('addresses')
            addresses = [[str(address) for address in obj.addresses.all()] for obj in qs]
        self.assertEqual(addresses, [[str(self.author_address)], [], []])
            addresses = [[str(address) for address in obj.addresses.all()] for obj in qs]
        self.assertEqual(addresses, [[str(self.author_address)], [], []])
  
      def test_foreignkey_to_inherited(self):
          with self.assertNumQueries(2):
              qs = BookReview.objects.prefetch_related('book')
              titles = [obj.book.title for obj in qs]
keep keep keep keep replace replace keep keep keep keep keep
 Refs #23919 -- Removed six.<various>_types usage

Thanks Tim Graham and Simon Charette for the reviews. 
tests/prefetch_related/tests.py