Question

I am writing a view that drives the “submit” button on a blog post editing page. This view will be capturing POST data from the form on the blog post edit page and updating the Post object associated with that blog post.

I am fairly new to Django, and just a little bit less new to Python, so I am unsure of the best way to simplify this view.

Just to make this a little easier to understand, draft is what I am calling blog posts when in the context of editing. The code I have now (reproduced in full below) has a series of 3 of blocks like this:

try:
    new_title = request.POST['post_title']
except (KeyError):
    return render_to_response('blog/edit.html', {
        'draft': draft,
        'error_msg': "That's weird. You didn't provide a" +
                        "post title in the POST arguments.",
        }, context_instance=RequestContext(request))
draft.title = new_title
# Here goes some code specific to handling updating the title

As you can see, basically, this block just tries to get POST data, and if it can’t, it redirects back to the edit page with an error message.

Since this view essentially does the same thing 3 times, it’s in violation of the DRY principle. I am trying to find a way to fix this. The problem with separating this code into another function is that the error handling process needs to return something to the caller of the view. Should I just separate it anyway and check the type of the return value? Is that clean? Won’t I have to pass a large number of arguments to the function? Is that considered bad form?

Also, if you have any other tips for improving the style or design of this code, I would greatly appreciate them, since I am very much a Python/Django newbie.

Thanks so much!

---

Full view code right now:

def save_changes(request, draft_id):
    draft = get_object_or_404(Post, pk=draft_id)
    # Get the new title
    try:
        new_title = request.POST['post_title']
    except (KeyError):
       return render_to_response('blog/edit.html', {
            'draft': draft,
            'error_msg': "That's weird. You didn't provide a" +
                            "post title in the POST arguments.",
            }, context_instance=RequestContext(request))
    draft.title = new_title
    if draft.slug = None:
        draft.slug = unique_slugify(draft.title)
    # Get the new text
    try:
        new_text = request.POST['post_text']
    except (KeyError):
        return render_to_response('blog/edit.html', {
            'draft': draft,
            'error_msg': "That's weird. You didn't provide" +
                            "post text in the POST arguments.",
            }, context_instance=RequestContext(request))
    draft.text = new_text
    # Get the new publication status
    try:
        new_published_status = request.POST['publish']
    except (KeyError):
        return render_to_response('blog/edit.html', {
            'draft': draft,
            'error_msg': "That's weird. You didn't provide a" +
                            "publication status in the POST arguments."
    if new_published_status != draft.published:
        if draft.published:
            draft.published = False
            draft.pub_date = None
        else:
            draft.published = True
            draft.pub_date = timezone.now()
    draft.save()
    return HttpResponseRedirect(reverse('blog.views.edit', args=draft.id))

Answer 1

A simple list comprehension will solve your issues.

error_messages = {'post_title':'post title','post_text':'post text','publish':'publication status'}
errors = [error_messages[key] for key in ('post_title','post_text','publish') if not request.POST.has_key(key)]

This will give you a list of the error message names. You can then write one error section taking the errors list and decide what to do with it (such as display all of them, display the first, or even do some fancy logic with the grammar of the message based on how many are missing).

May I recommend the Forms object in Django to do the validation for you?