          if self._routers is None:
              self._routers = settings.DATABASE_ROUTERS
          routers = []
          for r in self._routers:
              if isinstance(r, six.string_types):
                  router = import_string(r)()
              else:
                  router = r
              routers.append(router)
          return routers
 
</s> remove             lists = [[six.text_type(r) for r in a.first_book.read_by.all()]
 </s> add             lists = [[str(r) for r in a.first_book.read_by.all()] </s> remove             lists = [[[six.text_type(r) for r in b.read_by.all()]
 </s> add             lists = [[[str(r) for r in b.read_by.all()] </s> remove             lists = [[[six.text_type(r) for r in b.read_by.all()]
 </s> add             lists = [[[str(r) for r in b.read_by.all()] </s> remove             lists = [[[six.text_type(r) for r in b.read_by.all()]
 </s> add             lists = [[[str(r) for r in b.read_by.all()] </s> remove             lists = [[six.text_type(r) for r in b.read_by.all()] for b in author.books.all()]
 </s> add             lists = [[str(r) for r in b.read_by.all()] for b in author.books.all()]
            if isinstance(r, str):
          if self._routers is None:
              self._routers = settings.DATABASE_ROUTERS
          routers = []
          for r in self._routers:
            if isinstance(r, str):
                  router = import_string(r)()
              else:
                  router = r
              routers.append(router)
          return routers
keep keep keep keep replace keep keep keep keep keep
 Refs #23919 -- Removed six.<various>_types usage

Thanks Tim Graham and Simon Charette for the reviews. 
django/db/utils.py