I'm using a OpenERP V7. I want to make a button invisible when it is not a specific user how can i do this? I'm trying to wrap the buttons in a group and assign attr invisible to it, so far it has not worked for me.

<group attrs="{'invisible' : [('req_department.manager_id.id','!=',user.id)]}">
                        <button name="department_change_accept_accepted" string="Accept" states="accepted" type="workflow" groups="base.group_hr_manager"/>
                        <button name="department_change_reject_accepted" string="Reject" states="accepted" type="workflow" groups="base.group_hr_manager"/>
                        </group>