I'm new to OpenERP, I have following:

shipment_obj = self.pool.get('stock.picking.in').browse(cr, uid, context.get('active_id'))

this returns incoming shipment_obj, I can access fields/properties, but when I try to access one2many field "move_lines", and iterate over it, it returns None type object.

  for product in shipment_obj.move_lines:
     etc...

Here is original fields from OpenERP stock.py:

'move_lines': fields.one2many('stock.move', 'picking_id', 'Internal Moves', states={'done': [('readonly', True)], 'cancel': [('readonly', True)]}),
'product_id': fields.related('move_lines', 'product_id', type='many2one', relation='product.product', string='Product'),

I want to be able to get the products for this incoming shipment.

What is correct syntax to use for iterating over?

Thanks for feedback!