Hi,

in python use context as :

id_you_want = context.get('active_id', False) => return id or False

but the form should be saved at leat one time to create id.

to give id of the sale order form to sale order line tree one2many :

in sale order line do :

in xml : ....

<notebook>
<page string="Order Lines">
    <field name="order_line" context="{'order_id': active_id}">
        <form string="Sales Order Lines" version="7.0">
            <field name="order_id">

....

in python :

to get order id as default value, add this in python class sale order line :

_defaults = {
   'order_id': lambda self, cr, uid, context: context.get('order_id', False),}

each time you will click on create button in sale order line, order_id will have id of its parent form.

Bye