Compute the cumulative sum of a list until a zero appears

Question

I have a (long) list in which zeros and ones appear at random:

list_a = [1, 1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 1]

I want to get the list_b

Answer 1

I would use a generator if you want performance (and it's simple too).

def weird_cumulative_sum(seq):
    s = 0
    for n in seq:
        s = 0 if n == 0 else s + n
        yield s

list_b = list(weird_cumulative_sum(list_a_))

I don't think you'll get better than that, in any case you'll have to iterate over list_a at least once.

Note that I called list() on the result to get a list like in your code but if the code using list_b is iterating over it only once with a for loop or something there is no use converting the result to a list, just pass it the generator.