i get this error everytime i want to add a new line in stock.move.line

'qty_qty': line.qty_qty,
UnboundLocalError: local variable 'line' referenced before assignment

here is my code 

qty_qty = fields.Float('Quantity', compute="_multiplication_qty")

def _multiplication_qty(self):
        for order in self:
            qty_qty = 0.0
            for line in order.picking_id.move_line_ids_without_package:
                weight = line.product_id.weight
                if line.qty_done:
                    line.qty_qty = (line.qty_done * 100) / weight
        order.update({
            'qty_qty': line.qty_qty,
            })




~~~~~~~~~/xml~~~~~~
 <record id="view_stock_mov" model="ir.ui.view"> 
    <field name="name">stock.inherit</field>     
    <field name="model">stock.move.line</field> 
    <field name="inherit_id" ref="stock.view_stock_move_line_detailed_operation_tree"/>     <field name="arch" type="xml"> 
        <xpath expr="//field[@name='lot_id']" position="after"> 
        <field name="qty_qty" /> 
        </xpath> 
    </field> 
</record>