def get_sn(unit):
    """获取文本行的句子数量

    Keyword arguments:
    unit                    -- 文本行
    Return:
        sn                  -- 句数
    """
    sn = 0
    match_re = re.findall(str(sentence_delimiters), unit)
    if match_re:
        string = ''.join(match_re)
        sn = len(string)
    return int(sn)