from django.db.models import Q

    return reduce(lambda x, y: x | y,

                  [Q(**{field_name: x.id}) for x in objs])

def last_name(person):

    return person.formal_name.rpartition(' ')[2]

def custom_index(request, queryset, *args, **kwargs):

    """Blog list view that allows scrolling and also shows an index by

    year.

    """

    date_field = kwargs['date_field']

    if not kwargs.get('allow_future', False):

        queryset = queryset.filter(**{'%s__lte' % date_field: datetime.now()})

    authors = []

    if 'author' in request.GET:

        authors = [get_object_or_404(Person, username=author)

                   for author in request.GET.getlist('author')]

        extra_context['authors'] = authors

        queryset = queryset.filter(OR_filter('author', authors))

    tags = []

        extra_context['tags'] = tags

        queryset = queryset.filter(OR_filter('tags', tags))

    if authors or tags:

        query_string = '&'.join(['author=%s' % a.username for a in authors]

                                + ['tag=%s' % t.slug for t in tags])

        extra_context['query_string'] = query_string

    else:

        date_list = queryset.dates(date_field, 'year')

        extra_context['date_list'] = date_list

    paginate_by = kwargs.get('paginate_by', 6)  # Show 6 news items per page, by default

    paginator = Paginator(queryset, paginate_by)

    page = request.GET.get('page')

    try:

        blog_entries = paginator.page(page)

    except PageNotAnInteger:

        # If page is not an integer, deliver first page.

        blog_entries = paginator.page(1)

    except EmptyPage:

        # If page is out of range (e.g. 9999), deliver last page of results.

        blog_entries = paginator.page(paginator.num_pages)

    extra_context['blog_entries'] = blog_entries