Hi Arjun,

You want to get the sum of costs in expense records, that related to an expenditure right? Try like the following:

class expenditure_records(osv.Model):
    _name="expenditure.records"
    _columns={
    'name':fields.char('Expense name'),    
    'cost':fields.float('Expenditure cost'),
    'expense_id':fields.many2one('expenditure','Expense ID'),
    }
class expenditure(osv.Model):
    _name="expenditure"
    def _get_total(self, cr, uid, ids,field_name, args, context=None):
        expenditure_pool = self.pool.get('expenditure')
        res = {}
        for exp_id in self.browse(cr, uid, ids, context=context):
            s_total = 0
            exp = expenditure_pool.browse(cr,uid, exp_id.id, context=None)
            for line in exp.expense_ids:
                s_total += line.cost
            res[exp_id.id] = s_total
        return res
    _columns={
    'name':fields.char('Expense'),
    'date': fields.date(string="Date"),
    'expense_ids':fields.one2many('expenditure.records', 'expense_id', string="Expenses"),
    'total_expense':fields.function(_get_total, type="float", string="Total Expenses")
    }