Hello, i'm on Odoo 8, with locations activated.

When i proceed to my stock picking, i assign my products. If i have the quantities in stock no problem.
But sometimes the location has less quantities than the qty ordered, so i want to force transfer (and do internal transfer later). 

On products it's possible the same emplacement is forced in negative quantities, but it's possible another location is taken (actually the first product's location).

So i want to know how does works the "force system". I only see this in the code :

(picking class)

for pick in self.browse(cr, uid, ids, context=context):
    move_ids = [x.id for x in pick.move_lines if x.state in ['confirmed', 'waiting']]
    self.pool.get('stock.move').force_assign(cr, uid, move_ids, context=context)
#pack_operation might have changed and need to be recomputed
self.write(cr, uid, ids, {'recompute_pack_op': True}, context=context)
return True

(and move class)

return self.write(cr, uid, ids, {'state': 'assigned'}, context=context)

Is it the recompute_pack_op which get a new quant ? 

Is a function triggers when recompute_pack_op change ?

I don't understant anything with this recompute_pack_op , help me please