困扰了半天的一段代码

 

 # 根据给定的年月日以数字形式打印出日期

months = [
    'January',
    'February',
    'March',
    'April',
    'May',
    'June',
    'July',
    'August',
    'September',
    'October',
    'November',
    'December',
]
# 以1~31的数字作为结尾的列表
endings = ['st','nd','rd'] + 17 * ['th']\
            + ['st','nd','rd'] + 7 * ['th']\
            + ['st']

year    = raw_input('Year: ')
month   = raw_input('Month(1-12): ')
day     = raw_input('Day(1-31): ')

month_number = int(month)
day_number = int(day)

# 记得要将月份和天数减1，以获得正确的索引
month_name = months[month_number-1]
ordinal = day + endings[day_number-1]

print month_name + ' ' + ordinal + ', ' + year

endings 这行代码困扰了很久，一直不明白定义的endings变量赋值后面为什么要加上17*和7*，不明白17 * ['th']、 7 * ['th']这两个表达式到底什么意思，思索了1个小时，一点头绪都没有，跟一个同样在学习python的同事研究了半天也没结果，后来在同事的启发下，百度了这行代码，果然不止我一人被困扰了，参考了几位同仁的答案后豁然开朗，原来答案是这样的：

原来该变量定义的是1-31这31个数的英文后缀，这31个数的英文是1:first 2:second 3:third 4:fourth 5:fifth 6:sixth 7:seventh 8:eighth 9:ninth 10:tenth 11:eleventh 12:twelfth 13:thirteenth 14:fourteenth 15:fifteenth 16:sixteenth 17:seventeenth 18:eighteenth 19:ninteenth 20:twentieth 21:twentyfirst 22:twenty-second 23:twenty-third 24:twenty-fourth 25:twenty-fifth 26:twenty-sixth 27;twenty-seventh 28:twenty-eighth 29:twenty-ninth 30:thirtieth 31:thirty-first   
其中在第一个 ['st','nd','rd']后面从fourth到twentieth一共是17个‘th’，然后是又一个['st','nd','rd']后面再从twenty-fourth到thirtieth一共是7个‘th’， 17 * ['th']的意思就是：给这个数据添加17个'th'字符串；例如

a=3*['a']和a=['a','a','a']是一样的。纠结了好久哇，原来这么简单