Hello at all, 

Thanks for your answer. Actually your solution works, BUT not for this special case: 

I want to modify the "Country" Field in the Partner Module. So actually what I want is to have a special Country as default when a user wants to create a new contact. 

Your mentioned solution works for the almost all fields, BUT not for country field. Any ideas why the country field is so special in that case?

so I tried this: 

_defaults = {
 'country_id': lambda self, cr, uid, context: self.pool.get('res.country').browse(cr, uid, self.pool.get('res.country').search(cr, uid, [('code','=','CO')]))[0].id,       
        'tdoc' : '13',
        }

Unfortunately this solution works only for the tdoc field, but not for the country :-( 

At least not in Odoo9

Any ideas?

Dominic,

You can use this as your answer..

This will set current user to your new record...

user_id = fields.Many2one('res.users','User', default=lambda self: self.env.user)