Django TypeError at /polls/1/vote/ _reverse_with_prefix() argument after * must be an iterable, not int

Question

This is the polls app tutorial from the Django Docs.

When I go to the first question http://127.0.0.1:8000/polls/1/, select an option and click 'Vote', I get the error message.

error message

views.py:

from django.http import HttpResponseRedirect
from django.shortcuts import get_object_or_404, render
from django.urls import reverse
from django.views import generic

from .models import Choice, Question


class IndexView(generic.ListView):
    template_name = 'polls/index.html'
    context_object_name = 'latest_question_list'

    def get_queryset(self):
        """Return the last five published questions."""
        return Question.objects.order_by('-pub_date')[:5]


class DetailView(generic.DetailView):
    model = Question
    template_name = 'polls/detail.html'


class ResultsView(generic.DetailView):
    model = Question
    template_name = 'polls/results.html'


def vote(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    try:
        # request.POST['choice'] returns ID of the selected choice as a string
        selected_choice = question.choice_set.get(pk=request.POST['choice'])
    except (KeyError, Choice.DoesNotExist):
        # Redisplay the question voting form.
        return render(request, 'polls/detail.html', {
            'question': question,
            'error_message': "You didn't select a choice.",
        })
    else:
        selected_choice.votes += 1
        selected_choice.save()
        # Always return a HttpResponseRedirect after successfully dealing with POST data.
        # This prevents the data from being posted twice if a user hits the Back button.
        return HttpResponseRedirect(reverse('polls:results', args=question_id, ))

polls/urls.py:

from django.urls import path

from . import views

app_name = 'polls'
urlpatterns = [
    path('', views.IndexView.as_view(), name='index'),
    path('<int:pk>/', views.DetailView.as_view(), name='detail'),
    path('<int:pk>/results/', views.ResultsView.as_view(), name='results'),
    path('<int:question_id>/vote/', views.vote, name='vote'),
]

polls/templates/polls/index.html:

{% if latest_question_list %}
    <ul>
        {% for question in latest_question_list %}
            <li><a href="{% url 'polls:detail' question.id %}">{{ question.question_text }}</a></li>
        {% endfor %}
    </ul>
{% else %}
    <p>No polls are available.</p>
{% endif %}

polls/templates/polls/detail.html:

<h1>{{ question.question_text }}</h1>

{% if error_message %}<p><strong>{{ error_message }}</strong></p>{% endif %}

<form action="{% url 'polls:vote' question.id %}" method="post">
    {% csrf_token %}
    {% for choice in question.choice_set.all %}
        <input type="radio" name="choice" id="choice{{ forloop.counter }}" value="{{ choice.id }}"/>
        <label for="choice{{ forloop.counter }}">{{ choice.choice_text }}</label><br>
    {% endfor %}
    <input type="submit" value="Vote"/>
</form>

polls/templates/polls/results.html:

<h1>{{ question.question_text }}</h1>

<ul>
    {% for choice in question.choice_set.all %}
        <li>{{ choice.choice_text }} -- {{ choice.votes }} vote{{ choice.votes|pluralize }}</li>
    {% endfor %}
</ul>

<a href="{% url 'polls:detail' question.id %}">Vote again?</a>

Can anyone please help?

Answer 1

The problem is that you write:

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

Now args is used for positional arguments, and there can be (in theory) multiple. So it should be a collection of items. For example:

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

Note: in the tutorial they write args=(question_id,). Now that is something different than args=question_id. In Python a (0, ) is not an integer, but a 1-tuple containing one element: 0. In short: the brackets matter.

But there is no need to do all this wrapping. Django has a shorcut redirect(…) ^[Django-doc], to build HttpResponseRedirects in a more convenient way:

    return redirect('polls:results', question_id)

This takes *args and **kwargs itself as positional and named arguments. So you can write it as if you were calling the view directly as function (with the name of the view in front).