My code is here and what i want to do is to calculate total sub total from item_seller_price if price_unit is 0... but when the code runs it didnt gave Description in purchase order neither Scheduled Date nor Subtotal

from openerp.osv import osv, fields
class purchase_order_line(osv.osv):
 _inherit ='purchase.order.line'
 _columns = {
 'item_seller_price' : fields.float('Item Seller Price'),
 }
 def _amount_all(self, cr, uid, ids, field_name, arg, context=None):
 res = {}
 cur_obj=self.pool.get('res.currency')
 for order in self.browse(cr, uid, ids, context=context):
 res[order.id] = {
 'amount_untaxed': 0.0,
 'amount_tax': 0.0,
 'amount_total': 0.0,
 }
 val = val1 = 0.0
 cur = order.pricelist_id.currency_id
 for line in order.order_line:
 price_unit = line.price_unit
 if line.item_seller_price != 0:
 price_unit = line.item_seller_price
 val1 += line.price_subtotal
 for c in self.pool.get('account.tax').compute_all(cr, uid, line.taxes_id, line.price_unit, line.product_qty, line.product_id, order.partner_id)['taxes']:
 val += c.get('amount', 0.0)
 res[order.id]['amount_tax']=cur_obj.round(cr, uid, cur, val)
 res[order.id]['amount_untaxed']=cur_obj.round(cr, uid, cur, val1)
 res[order.id]['amount_total']=res[order.id]['amount_untaxed'] + res[order.id]['amount_tax']
 return res
 def onchange_product_id(self, cr, uid, ids, pricelist_id, product_id, qty, uom_id,
 partner_id, date_order=False, fiscal_position_id=False, date_planned=False,
 name=False, price_unit=False, state='draft', context=None):
 value = {}
 if not product_id:
 return value
 value = super(purchase_order_line,self).onchange_product_id(cr, uid, ids, pricelist_id, product_id, qty, uom_id, partner_id, date_order, fiscal_position_id, date_planned, name, price_unit, state, context )
 names = self.pool.get('product.product').browse(cr, uid,product_id, context=context)
 value.update({
 'item_seller_price' : names.product_item_seller_price_id and names.product_item_seller_price_id.name or False,
 'name' : names.product_item_seller_price_id and names.product_item_seller_price_id.name or False,
# 'sitelocation': names.sitelocation and names.sitelocation.id or False, 
# 
 })
 return {'value' : value}
#purchase_order_line()
class purchase_order(osv.osv):
 _inherit ='purchase.order' 
 def _prepare_inv_line(self, cr, uid, account_id, order_line, context=None):
 """Collects require data from purchase order line that is used to create invoice line
 for that purchase order line
 :param account_id: Expense account of the product of PO line if any.
 :param browse_record order_line: Purchase order line browse record
 :return: Value for fields of invoice lines.
 :rtype: dict
 """
 return {
 'name': order_line.name,
 'account_id': account_id,
 'price_unit': order_line.price_unit or 0.0,
 'quantity': order_line.product_qty,
 'product_id': order_line.product_id.id or False,
 'item_seller_price':order_line.item_seller_price,
 'uos_id': order_line.product_uom.id or False,
 'invoice_line_tax_id': [(6, 0, [x.id for x in order_line.taxes_id])],
 'account_analytic_id': order_line.account_analytic_id.id or False,
 'purchase_line_id': order_line.id,
 }
 def action_invoice_create(self, cr, uid, ids, context=None):
 """Generates invoice for given ids of purchase orders and links that invoice ID to purchase order.
 :param ids: list of ids of purchase orders.
 :return: ID of created invoice.
 :rtype: int
 """
 context = dict(context or {})
 inv_obj = self.pool.get('account.invoice')
 inv_line_obj = self.pool.get('account.invoice.line')
 res = False
 uid_company_id = self.pool.get('res.users').browse(cr, uid, uid, context=context).company_id.id
 for order in self.browse(cr, uid, ids, context=context):
 context.pop('force_company', None)
 if order.company_id.id != uid_company_id:
 #if the company of the document is different than the current user company, force the company in the context
 #then re-do a browse to read the property fields for the good company.
 context['force_company'] = order.company_id.id
 order = self.browse(cr, uid, order.id, context=context)
 # generate invoice line correspond to PO line and link that to created invoice (inv_id) and PO line
 inv_lines = []
 for po_line in order.order_line:
 if po_line.state == 'cancel':
 continue
 acc_id = self._choose_account_from_po_line(cr, uid, po_line, context=context)
 inv_line_data = self._prepare_inv_line(cr, uid, acc_id, po_line, context=context)
 inv_line_id = inv_line_obj.create(cr, uid, inv_line_data, context=context)
 inv_lines.append(inv_line_id)
 po_line.write({'invoice_lines': [(4, inv_line_id)]})
 # get invoice data and create invoice
 inv_data = self._prepare_invoice(cr, uid, order, inv_lines, context=context)
 inv_id = inv_obj.create(cr, uid, inv_data, context=context)
 # compute the invoice
 inv_obj.button_compute(cr, uid, [inv_id], context=context, set_total=True)
 # Link this new invoice to related purchase order
 order.write({'invoice_ids': [(4, inv_id)]})
 res = inv_id
 return res
class invoice_line(osv.osv):
 _inherit ='account.invoice.line'
 _columns = {
 'item_seller_price' : fields.float('item seller price'),
 }