code: def entries_published(queryset):
      
      now = timezone.now()
      return queryset.filter(
          models.Q(start_publication__lte=now) |
          models.Q(start_publication=None),
          models.Q(end_publication__gt=now) |
          models.Q(end_publication=None),
          status=PUBLISHED, sites=Site.objects.get_current())
docs: Return only the entries published.