@api.onchange('name')
def _onchange_name(self):
    if self.name:
        self.event_ticket_ids.filtered((lambda ticket: (ticket.name == _('Registration')))).update({'name': (_('Registration for %s') % self.name)})
@api.onchange('name')
def _onchange_name(self):
    if self.name:
        self.event_ticket_ids.filtered((lambda ticket: (ticket.name == _('Registration')))).update({'name': (_('Registration for %s') % self.name)})