I am trying to add 30 days in date field in `sale.order` in **OpenERP v.7**
Actualy I did it but the problem is that I want that 30 days to be added on the date I choose in other date field not just to add a 30 days on today's date.

The Date field is `date_order`. When I choose a date, I want that 30 days to be added on the chosen date. In the code I make it to add that 30 days on today's date but I want it on the date I am choosing automatically to be changed 30 days later.

```
class Sale_Order(osv.Model):
    _inherit = 'sale.order'

_columns = {
    'duedate': fields.date('Duedate', readonly=True),

}
_defaults = {
    'duedate': (date.today() + timedelta(days=30)).strftime(DEFAULT_SERVER_DATE_FORMAT),
}

```

[![enter image description here](https://i.stack.imgur.com/ypZDA.png)](https://i.stack.imgur.com/ypZDA.png)

Can someone help me?

Thank you!