docs: def trade_day(dt, cal='US'):
      """
      Latest trading day w.r.t given dt
  
      Args:
          dt: date of reference
          cal: trading calendar
  
      Returns:
          pd.Timestamp: last trading day
  
      Examples:
          >>> trade_day('2018-12-25').strftime('%Y-%m-%d')
          '2018-12-24'
      """
      from xone import calendar
  
      dt = pd.Timestamp(dt).date()
      return calendar.trading_dates(start=dt - pd.Timedelta('10D'), end=dt, calendar=cal)[-1]