def QA_util_get_pre_trade_date(cursor_date, n=1):
    """
    得到前 n 个交易日 (不包含当前交易日)
    :param date:
    :param n:
    """

    cursor_date = QA_util_format_date2str(cursor_date)
    if cursor_date in trade_date_sse:
        return QA_util_date_gap(cursor_date, n, "lt")
    real_aft_trade_date = QA_util_get_real_date(cursor_date)
    return QA_util_date_gap(real_aft_trade_date, n, "lt")