Python - 序數轉換

忘了是在哪裡看到的，不常用，不過是一個滿有趣的寫法，利用python的dict，能將數字1變成1st，數字2變成2nd，數字3變成3rd，數字4變成4th等。

## Returns the ordinal number of a given integer, as a string. eg. 1 -> 1st, 2 -> 2nd, 3 -> 3rd, etc.
def ordinal(num):
    num = int(num)
    if 10 <= num % 100 < 20:
        return "{0}th".format(num)
    else:
        ords = {1 : "st", 2 : "nd", 3 : "rd"}.get(num % 10, "th")
        return "{0}{1}".format(num, ords)