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 the zip function to loop the values in pairs:

def special_sum(numbers):
    s = 0
    for (prev, current) in zip([None] + numbers[:-1], numbers):
        if prev != 13 and current != 13:
            s += current
    return s

or you can do a oneliner:

def special_sum(numbers):
    return sum(current for (prev, current) in zip([None] + numbers[:-1], numbers)
               if prev != 13 and current != 13)

You can also use iterators:

from itertools import izip, chain
def special_sum(numbers):
    return sum(current for (prev, current) in izip(chain([None], numbers), numbers)
               if prev != 13 and current != 13)

(the first list in the izip is longer than the second, zip and izip ignore the extra values).