views.py

def update_rsvp(request):
    if request.method == 'GET':
        person = Invitee.objects.get(code=request.session['code'])
        form = InviteeForm(instance=person)
    elif request.method == 'POST':
        form = InviteeForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect('invites:success')
        else:
            form = InviteeForm(request.POST)
    return render(request, 'invites/update.html', {'form': form})