“这是什么意思：key = lambda x：x [-1]？”

Question

I know that a.sort(key=lambda x: x[1]) means it sorts with respect to second element.
But x[-1] ??
Shouldn't there be only two configurations x[0] and x[1] ?
Or am I missing something obvious?
Lets consider a = [(10, 4), (3, 5), (7, 1)]

Answer 1

Python has the ability to index from the end of a list. Hence, x[-1] refers to the last element, x[-2] refers to the second to last element, etc.

a.sort(key=lambda x: x[-1]) 

will sort a by the last element.

>>> a = [(10, 4), (3, 5), (7, 1)]

>>> a.sort(key=lambda x: x[-1])
[(7, 1), (10, 4), (3, 5)]

Answer 2

您正在按每个元组的最后一个元素进行排序（即，分别按4、5、1而不是10、3、7进行排序）