Hi,

Refer this code

def onchange_chart_id(self, cr, uid, ids, chart_account_id=False, context=None):
    res = {}
    if chart_account_id:
        company_id = self.pool.get('account.account').browse(cr, uid, chart_account_id, context=context).company_id.id
        now = time.strftime('%Y-%m-%d')
        domain = [('company_id', '=', company_id), ('date_start', '<', now), ('date_stop', '>', now)]
        fiscalyears = self.pool.get('account.fiscalyear').search(cr, uid, domain, limit=1)
        res['value'] = {'company_id': company_id, 'fiscalyear_id': fiscalyears and fiscalyears[0] or False}
    return res