<report
 string="Delivery Slip"
 id="stock.action_report_delivery"
 model="stock.picking"
 report_type="qweb-pdf"
 name="stock.report_deliveryslip"
 file="stock.report_deliveryslip"
 print_report_name="'Delivery Slip - %s - %s' % (object.partner_id.name or '', object.name)"
 menu="False"
/>

def print(self):
    data = {
        'ids': self.picking_id.id,
        'model': self.picking_id._name,
        'form': {
            'group_by': self.group_by,
            'hide_prices': self.hide_prices,
        },
    }
    action = self.report.report_action([], data=data)
    action.update({'close_on_report_download': True})
    return action

Python expression on custom report 'print_report_name' not being evaluated while calling report_action, any ideas on how to add dynamic Printed report name with custom report?