code: def cache_infos(self, queryset):
          
          self.cache = {}
          for item in queryset:
              # If the sitemap is too slow, don't hesitate to do this :
              #   self.cache[item.pk] = (item.count, None)
              self.cache[item.pk] = (
                  item.count, TaggedItem.objects.get_by_model(
                      self.entries_qs, item)[0].last_update)
docs: Cache the number of entries published and the last
          modification date under each tag.