code: def cal_term_code(year, is_first_term=True):
      
      if year <= 2001:
          msg = '出现了超出范围年份: {}'.format(year)
          raise ValueError(msg)
      term_code = (year - 2001) * 2
      if is_first_term:
          term_code -= 1
      return '%03d' % term_code
docs: 计算对应的学期代码
  
      :param year: 学年开始年份,例如 "2012-2013学年第二学期" 就是 2012
      :param is_first_term: 是否为第一学期
      :type is_first_term: bool
      :return: 形如 "022" 的学期代码