Field not exist checking

[isergey]

    def render(self, context):
        key = self.queryset_var.var
        value = self.queryset_var.resolve(context)
        order_by = context['request'].field
        if len(order_by) > 1:
            try:
                try:
                    field_name = order_by
                    if order_by[0] == '-':
                        field_name = order_by[1:]
                    # check for order field exist in model
                    value.model._meta.get_field(field_name)
                    context[key] = value.order_by(order_by)
                except FieldDoesNotExist as e:
                    if settings.DEBUG == True:
                        raise e

            except template.TemplateSyntaxError:
                if INVALID_FIELD_RAISES_404:
                    raise Http404('Invalid field sorting. If DEBUG were set to ' +
                    'False, an HTTP 404 page would have been shown instead.')
                context[key] = value
        else:
            context[key] = value

        return ''