sum4.py

def sum4(list_integer):
    sum = 0
    i = 0
    length = len(list_integer)
    while i < length:
        sum += list_integer[i]
        if list_integer[i] == 4: i += 1
        i += 1
    return sum

print sum4([1, 2])
print sum4([3, 4])
print sum4([4, 5, 6])
print sum4([4, 9, 4, 9, 4, 9])
print sum4([])