如何使用切片运算符更改嵌套列表中的元素

Question

testlist = [1, 4, 9, 'sixteen', ['25', '...']]

我想使用切片运算符将嵌套列表的最后一个元素更改为36.我该怎么做？

Answer 1

You can do it as follows:

>>> testlist = [1 , 4 , 9 , 'sixteen ', ['25 ', '... ']]
>>> testlist[-1][-1] = '36'
[1, 4, 9, 'sixteen', ['25', '...', '36']]

If you simply want to add on as the last element instead of replace, do: testlist[-1].append('36') instead

In lists, the -1 index gets the last element of a list. However, if your nested list is not always last, you can do:

>>> testlist[i][-1] = '36

where i is the position of the nested list in testlist . More generally, you can do:

>>> testlist[i][j] = '36'

where i fetches the ith element in testlist and j fetches the jth element in the ith element.

Examples

>>> a = [[1,2],[3,4],[5,6]]    #note the nested lists
>>> a[1][1]
4
>>> a[-1][-1]
6
>>> a[-1][0]
5
>>> a[0][-1]
2