Python - 向后迭代列表中的范围

Question

I'd like to search backwards through a list

This is code that I read in other posts should work

ls = [1, 2, 3]

for i in range(len(ls)-1, 0, -1):
    print(i)

The output would be:

2
1

Wheras if I use this code:

ls = [1, 2, 3]

for i in range(len(ls)-1, -1, -1):
    print(i)

The output is:

2
1
0

Why is it that range(len(ls)-1, 0, -1) skips an element, and why is it recommended as a solution for backwards iteration (rather than range(len(ls)-1, -1, -1) )?

Answer 1

If you don't mind the index being negative, you can do:

a = [1,2,3]
for i in range(-1, -1*(len(a)+1), -1):
    print(i, a[i])