In OpenERP first we create the product and then calculates the quantity of product. In product form picking Id is generated and picking id will return to the value of this product and then product will calculated automatically in stock.

Use this function given below

def product_confirm(self, cr, uid, ids):
     
        picking_id = super(mrp_production,self).action_confirm(cr, uid, ids)
        for production in self.browse(cr, uid, ids):
            source = production.product_id.product_tmpl_id.property_stock_production.id
            if not production.bom_id:
                continue
            for sub_product in production.bom_id.sub_products:
                qty1 = sub_product.product_qty
                qty2 = production.product_uos and production.product_uos_qty or False
                if sub_product.subproduct_type == 'variable':
                    if production.product_qty:
                        qty1 *= production.product_qty / (production.bom_id.product_qty or 1.0)
                    if production.product_uos_qty:
                        qty2 *= production.product_uos_qty / (production.bom_id.product_uos_qty or 1.0)
                data = {
                    'name': 'PROD:'+production.name,
                    'date': production.date_planned,
                    'product_id': sub_product.product_id.id,
                    'product_qty': qty1,
                    'product_uom': sub_product.product_uom.id,
                    'product_uos_qty': qty2,
                    'product_uos': production.product_uos and production.product_uos.id or False,
                    'location_id': source,
                    'location_dest_id': production.location_dest_id.id,
                    'move_dest_id': production.move_prod_id.id,
                    'state': 'waiting',
                    'production_id': production.id
                }
                self.pool.get('stock.move').create(cr, uid, data)
        return picking_id