Update of Magento stock quantity: reduced the memory footprint and improved...

performance by using read() instead of browse() and proceeding by steps of 1000
records at a time.

Bug report: https://code.launchpad.net/bugs/1330450
Original MP: https://code.launchpad.net/~camptocamp/openerp-connector-magento/7.0-update-stock-1330450/+merge/223393
The call on 157 does not need additional fields so it does not use this attribute.
If one want to pass additional fields, it can inherit the model and something along these lines:

    def _recompute_magento_qty_backend(self, cr, uid, backend, products, 
                                                                     read_fields=None, context=None):
        return super(magento_product_product, self)._recompute_magento_qty_backend(
            self, cr, uid, backend, products, read_fields=['field1', 'field2'], context=context)