python-Django UnboundLocalError

我有一个简单的表单集，用于将捐赠者注册到我的数据库。

如果我登陆页面上来自 DB 的现有条目并从表单输入中删除一个值并提交，我会得到一个 UnboundLocalError。

Django Version: 1.3 

Exception Type: UnboundLocalError 

Exception Value: local variable 'dac' referenced before assignment 

views.py

@login_required

def dizimista(request, nr_dizimista):

    dizimista = get_object_or_404(CadastroDizimista, pk=nr_dizimista, usuario=request.user)

    if request.method == 'POST' and request.POST.get('action') == 'Cancelar':

        return HttpResponseRedirect("/lista/")

    elif request.method == 'POST' and request.POST.get('action') == 'Salvar':

        form = FormCadastroDizimista(request.POST, request.FILES, instance=dizimista)

        if form.is_valid():

            cadastro = form.save(commit=False)

            cadastro.usuario = request.user

            cadastro.save()

            return HttpResponseRedirect("/lista/")

    else:

        form = FormCadastroDizimista(instance=dizimista)

        dac = CadastroDizimista.objects.get(pk=nr_dizimista).datacadastro

        dam = CadastroDizimista.objects.get(pk=nr_dizimista).datamodificado

    return render_to_response("cadastro.html", {'dac': dac, 'dam': dam, 'form': form}, context_instance=RequestContext(request))