code

def _add_product(self, product, qty=0.0):
        # corresponding_line = self.line_ids.filtered(lambda r: r.product_id.id == product.id and (self.scan_location_id.id == r.location_id.id or not self.scan_location_id))
        StockQuant = self.env['stock.quant']
        company_id = self.company_id.id
        if not company_id:
            company_id = self._uid.company_id.id
        dom = [('company_id', '=', company_id), ('location_id', '=', self.scan_location_id.id or self.location_id.id), ('lot_id', '=', False),
                    ('product_id','=', product.id), ('owner_id', '=', False), ('package_id', '=', False)]
        quants = StockQuant.search(dom)
        th_qty = sum([x.quantity for x in quants])
        seq_val = self._set_sequence()
        self.line_ids += self.line_ids.new({
            'location_id': self.scan_location_id.id or self.location_id.id,
            'product_id': product.id,
            'product_uom_id': product.uom_id.id,
            'theoretical_qty': th_qty,
            'product_qty': 0,
            'line_sequence': seq_val,
        })
        return True