I'm using OpenERP v7 and requesting this below output in Purchase order line window

PO0001      PO0002    PO0003  
  Line      Line      Line
  10          10        10
  20          20        20
  30                    30

My code:

_columns={
'line_no':fields.function(_get_line_no,string='Line No',type='integer', multi="lineno",store=True),
'next_line_no':fields.function(_get_line_no,string='Next Line No',type='integer', multi="lineno", store=True),
}
_defaults = {
    'next_line_no':10,
    'line_no':0,   
}
def _get_line_no(self, cr, uid, ids, name, arg, context=None):
  res = {}
  nextno =0
  total =0
  for record in self.browse(cr, uid, ids, context=context):                             
    no = record.next_line_no        
    next_no = nextno + no
    total += next_no
    res[record.id]={
              'next_line_no':next_no,
              'line_no': total,                                 
    }        
  return res

But im getting this kind of output . Any advice would be greatful.

PO0001      PO0002    PO0003  
  Line      Line      Line
  10          40        60
  20          50        70
  30                    80

Anyone could help me to achive the required output.