Skipping elements in a List Python

Question

I\'m new to programming and I\'m trying to do the codingbat.com problems to start. I came across this problem:

Given an array calculate the sum except when there is

Answer 1

You can use while loop to treat multiple 13.

def sum13(lis):
    while pos(lis):
        if pos(lis) == len(lis) - 1:
            lis = lis[:pos(lis)]
        else:
            lis = lis[:pos(lis)]+lis[pos(lis)+1:]

    return sum(lis)