I am trying to extend a bit product and sale modules, yet in version 6.1 In some onchange functions in sale_order_line, I call a method in product.product. Something like this:

 def _compute_qty_swap_uom_uos(self, cr, uid,
                                  product_id, swap_type='uom2uos', from_uom_id=False,
                                  qty=False, to_uom_id=False, context=None):

There, I pass the new, actual values from a form (product_id, from_uom_id, qty, to_uom_id). Then, inside this method, I try to check if the product itself has an 'uos_id' defined or not, like this:

product_obj = self.pool.get('product.product')
product = product_obj.browse(cr, uid, product_id, context=context)
def_uos_id = product.uos_id
_logger.debug('[_compute_price_swap_uom_uos]  def_uos_id = {}'.format(def_uos_id))

if not def_uos_id or not product.uos_coeff:
    pass  # whatever things to do

But no matter what, I am not able to access it and I get this message:

(...)
 File "/opt/openerp/testing/openerp_61_ocb_devel/all-addons/product_list_price_uos/product.py", line 64, in _compute_qty_swap_uom_uos
    def_uos_id = product.uos_id
AttributeError: 'browse_record_list' object has no attribute 'uos_id'

I have also tried with:

def_uos_id = product.uos_id.id

with same result.

Variable 'uos_id' is in product.template, but I should be able to access it through product.product due to inheritance. In fact, I am not even able to access product.product variables, like 'price'.

What am I missing or doing plainly wrong?