有没有一种方法可以获取2d列表中某项的索引？ -Python

Question

假设我有一个二维列表：

 a = [[0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
     [10, 11, 12, 13, 14, 15, 16, 17, 18, 19],
     [20, 21, 22, 23, 24, 25, 26, 27, 28, 29],
     [30, 31, 32, 33, 34, 35, 36, 37, 38, 39],
     [40, 41, 42, 43, 44, 45, 46, 47, 48, 49],
     [50, 51, 52, 53, 54, 55, 56, 57, 58, 59],
     [60, 61, 62, 63, 64, 65, 66, 67, 68, 69],
     [70, 71, 72, 73, 74, 75, 76, 77, 78, 79],
     [80, 81, 82, 83, 84, 85, 86, 87, 88, 89],
     [90, 91, 92, 93, 94, 95, 96, 97, 98, 99]]

基本上，我想要做的就是以元组形式获取列表中任何项目的索引：

>>> some_function(a, 55) # index of 55 is a[5][5]
(5, 5)
>>> some_function(a, 67) # index of 67 is a[6][7]
(6, 7)

很遗憾，a.index(55)不起作用：

>>> a.index(55)
Traceback (most recent call last):
  File "<pyshell#7>", line 1, in <module>
    a.index(55)
ValueError: 55 is not in list

有没有一种快速简便的方法？