class EarnPeriods(OperationsList, FormView):
    form_class = forms.DateForm
    template_name = 'period.html'
    earn = True
    def post(self, request, *args, **kwargs):
        context = self.get_context_data()
        context['e'] = True
        context['user_username'] = request.user.username
        if context['form'].is_valid:
            date_start = datetime.datetime.strptime(request.POST['date_start'], '%d.%m.%Y').date()
            date_end = datetime.datetime.strptime(request.POST['date_end'], '%d.%m.%Y').date()
            earnings_list = super(EarnPeriods, self).get_queryset().filter(date__range=(date_start, date_end), sum__gt=0)
            summa = earnings_list.aggregate(Sum('sum'))
            context['earnings_list'] = earnings_list
            context['summa'] = check_none(summa['sum__sum'])
        return super(FormView, self).render_to_response(context)
    def get_context_data(self, **kwargs):
        context = super(EarnPeriods, self).get_context_data(**kwargs)
        form = self.get_form(self.form_class)
        context['form'] = form
        return context

if context['form'].is_valid():