How to obtain the last index of a list?

Question

Suppose I\'ve the following list:

list1 = [1, 2, 33, 51]
                    ^
                    |
indices  0  1   2   3

How do I obtain the

Answer 1

all above answers is correct but however

a = [];
len(list1) - 1 # where 0 - 1 = -1

to be more precisely

a = [];
index = len(a) - 1 if a else None;

if index == None : raise Exception("Empty Array")

since arrays is starting with 0