def vote(request, poll_id):
    p = get_object_or_404(Poll, pk=poll_id)
    try:
        selected_choice = Choice.objects.get(poll_id=p.pk, pk=request.POST['choice'])
    except (__HOLE__, Choice.DoesNotExist):
        # Redisplay the poll voting form.
        return render_to_response('polls/detail.html', {
            'poll': p,
            'error_message': "You didn't select a choice.",
        }, context_instance=RequestContext(request))
    else:
        Choice.objects.filter(pk=pk, poll_id=p.pk).update(votes=F('votes') + 1)
        # Always return an HttpResponseRedirect after successfully dealing
        # with POST data. This prevents data from being posted twice if a
        # user hits the Back button.
        return HttpResponseRedirect(reverse('polls:results', args=(p.id,)))
dataset/ETHPy150Open disqus/sharding-example/polls/views.py/vote