how to change subject in odoo email template?

I am using project issue module from odoo 10, its using notification template email to send notification.

here is default notification email tempelate

<record id="mail_template_data_notification_email_default" model="mail.template">
        <field name="name">Notification Email</field>
        <field name="subject"> ${object.subject or (object.record_name and 'Re: %s' % object.record_name ) or (object.parent_id and object.parent_id.subject and 'Re: %s' % object.parent_id.subject) or (object.parent_id and object.parent_id.record_name and 'Re: %s' % object.parent_id.record_name)}</field>
        <field name="model_id" ref="mail.model_mail_message"/>
        <field name="auto_delete" eval="True"/>

so how to put ticket id (project issue id) to subject email? I try this

<field name="subject"> Ticket# ${object.task_id} ${object.subject or (object.record_name and 'Re: %s' % object.record_name ) or (object.parent_id and object.parent_id.subject and 'Re: %s' % object.parent_id.subject) or (object.parent_id and object.parent_id.record_name and 'Re: %s' % object.parent_id.record_name)}</field>

because in project.issue task_id is the ticket id, but it didn't work.

please help