[Solved]-DJANGO – local variable 'form' referenced before assignment

The Django docs handle this, but slightly differently from the other answers. See https://docs.djangoproject.com/en/dev/topics/forms/#using-a-form-in-a-view

Using an else, if the request is not POST then create the blank form. The below is pasted directly from the docs.

def get_name(request):
    # if this is a POST request we need to process the form data
    if request.method == 'POST':
        # create a form instance and populate it with data from the request:
        form = NameForm(request.POST)
        # check whether it's valid:
        if form.is_valid():
            # process the data in form.cleaned_data as required
            # ...
            # redirect to a new URL:
            return HttpResponseRedirect('/thanks/')

    # if a GET (or any other method) we'll create a blank form
    else:
        form = NameForm()

    return render(request, 'name.html', {'form': form})

If there can be so to say – collateral damage by initializing an empty form , then you may also provide a dummy value as a filler , till the request.POST is initialized …

def contato(request):
    form = "Dummy String"
    form_class = ContactForm

    # if request is not post, initialize an empty form
    #form = form_class(request.POST or None) # Maybe Not 

    form = form_class(request.POST) # Instead 
    if request.method == 'POST':
        if form.is_valid():
            nome = request.POST.get('nome')
            email = request.POST.get('email')
            msg = request.POST.get('msg')

            send_mail('Subject here', msg, email, ['testmail@gmail.com'], fail_silently=False)
            return HttpResponseRedirect('blog/inicio')
    return render(request, 'blog/inicio.html', {'form': form})

The only issue you have is you did not declare ContactForm as function,
change FROM this;

def contato(request):
    form_class = ContactForm
    if request.method == 'POST':

TO;

def contato(request):
    form_class = ContactForm()
    if request.method == 'POST':