title: invalid literal for int() with base 10: 'on' Python-Django
body: <p>i am learning django from official django tutorial. and i am getting this error when vote something from form. this caused from - probably - vote function under views.py </p>
  
  <p>here is my views.py / vote function : </p>
  
  <pre><code>def vote(request,poll_id):
      p=get_object_or_404(Poll, pk=poll_id)
      try:
              selected_choice = p.choice_set.get(pk=request.POST['choice'])
      except (KeyError, Choice.DoesNotExist):
              return render_to_response('polls/detail.html', {'poll':p,
                                                              'error_message' : "didint select anything ",}, context_instance= RequestContext(request))
  
      else:
              selected_choice.votes += 1
              selected_choice.save()
              return HttpResponseRedirect(reverse('polls.views.results', args=(p.id,)))
  </code></pre>
  
  <p>and this is error message screen : </p>
  
  <blockquote>
    <p>**ValueError at /polls/2/vote/</p>
    
    <p>invalid literal for int() with base 10: 'on'**</p>
    
    <p>Request Method:   POST Request URL:   127.0.0.1:8000/polls/2/vote/</p>
    
    <p>Django Version:   1.4 Exception Type: ValueError Exception Value: 
    invalid literal for int() with base 10: 'on' Exception
    Location: /usr/local/lib/python2.7/dist-packages/django/db/models/fields/<strong>init</strong>.py
    in get_prep_value, line 537</p>
  </blockquote>
  
  <p>and here is my polls/urls.py : </p>
  
  <pre><code>from django.conf.urls import patterns, include, url
  </code></pre>
  
  <p>urlpatterns = patterns('polls.views',</p>
  
  <pre><code>    url(r'^$', 'index'),
      url(r'^(?P&lt;poll_id&gt;\d+)/$','detail'),
      url(r'^(?P&lt;poll_id&gt;\d+)/results/$','results'),
      url(r'^(?P&lt;poll_id&gt;\d+)/vote/$','vote'),
  </code></pre>
  
  <p>)</p>
  
  <p>and here is project/urls.py : </p>
  
  <pre><code>from django.conf.urls import patterns, include, url
  </code></pre>
  
  <p>urlpatterns = patterns('polls.views',</p>
  
  <pre><code>    url(r'^$', 'index'),
      url(r'^(?P&lt;poll_id&gt;\d+)/$','detail'),
      url(r'^(?P&lt;poll_id&gt;\d+)/results/$','results'),
      url(r'^(?P&lt;poll_id&gt;\d+)/vote/$','vote'),
  </code></pre>
  
  <p>)</p>