def _add_numbers(self, cr, uid, ids, field_name, arg, context=None):

res = {}

for record in self.browse(cr, uid, ids, context=context):

       res[record.id] = record.number1 + record.number2

return res

'number1':fields.float('First Value'),

'number2':fields.float('Second Value'),

'result':fields.function(_add_numbers,method= True,type='float',string='Result'),