How to show particular purchase order total price in my custom module I am creating a function for show amount_total iin my custom module but it's not showing

def create(self, cr, uid, vals, context=None):
if vals.get('buy_back'):
    purchase_obj=self.pool.get('purchase.order')
    sequence=self.pool.get('ir.sequence').get(cr, uid, 'purchase.order')
    new_purchase=purchase_obj.create(cr, uid, {'name':sequence,'amt_total':vals.get('amount_total')}, context=context)
    import pprint
    pprint.pprint( vals )
    print 'amount_total'
    vals['purchase_order']=new_purchase
    pprint.pprint( vals )

this is my view file

                <field name="buy_back"/>
                <field name="purchase_order"/>
                <fiels name="amt_total"/>
            </xpath>