using rstrip on form.cleaned_data[i] in Django

In my views.py, i have a snippit of code like this:

def clean_post_data(form):
    for i in form.cleaned_data:
        form.cleaned_data[i] = form.cleaned_data[i].rstrip()

def add_product(request):   
    form = ProductForm(request.POST, request.FILES or None)
    image = Image.objects.all()
    action = "Add"

    if request.POST:
        if form.is_valid():
            clean_post_data(form)
            form.save()
            action = "Added new product"
            return render_to_response('cms/admin/action.html', {'action' : action},context_instance=RequestContext(request))
        else:
            action = "There was an error. Please go back and try again"
            return render_to_response('cms/admin/action.html', {'action' : action}, context_instance=RequestContext(request))

    return render_to_response('cms/admin/editproduct.html', {'form' : form, 'action' : action, 'image' : image}, context_instance=RequestContext(request))

But when i run that, i get the following error 'list' object has no attribute 'rstrip'. What am i doing wrong.

I originally had the for i in form.cleaned_data: loop directly in the view (not in another function) and it worked fine, but now when i try it i get the same error as above. http://dpaste.com/92836/