Question

I don’t think I’ve seen anything that says you’re not allowed to do this (or that your are), but is there any reason you shouldn’t? It seems to work fine.

def get_page(request, topic_slug = 'home', tag_slug = None, form = None):

    #...

    if form is None:
        form = CommentForm()
    d = {'topic':topic, 'topics':topics, 'tags':tags, 'comments':comments, 'form':form}

    d.update(csrf(request))
    return render_to_response('page.html', d)

def save_comment(request, topic_slug):

    if request.method == 'POST':
        form = CommentForm(request.POST)

        if form.is_valid():
            #...save
        else:
            kwargs = {'topic_slug':topic_slug}
            kwargs['form'] =form
            return get_page(request, **kwargs) #<-------------- this

    return HttpResponseRedirect(reverse('get_page', kwargs = {'topic_slug':topic_slug}))

Answer 1

render_to_response is just a shortcut. Result of calling it is still HttpResponse‘s instance.

As a proof, see render_to_response()‘s declaration in source of Django:

def render_to_response(*args, **kwargs):
    """
    Returns a HttpResponse whose content is filled with the result of calling
    django.template.loader.render_to_string() with the passed arguments.
    """
    httpresponse_kwargs = {'mimetype': kwargs.pop('mimetype', None)}
    return HttpResponse(loader.render_to_string(*args, **kwargs),
        **httpresponse_kwargs)

Pretty self-explanatory.

By writing this:

return get_page(request, **kwargs)

you actually do something like:

return render_to_response(request, kwargs)

(but with slightly altered kwargs argument).