Error in Django Tutorial # 4

[Frank Claessen]

On page 49 part of views.py is changed and at the end of

def vote ...:

there is a redirect as follows:

return HttpResponseRedirect(reverse('polls:results', args=(question.id,)))

There is an error however that shows that question.id is in fact empty
The correct line therefore has to be:

return HttpResponseRedirect(reverse('polls:results', args=(question_id,)))

The error is caused by the reverse part by the way, not by the redirect