How to find the cumulative sum of numbers in a list?

Question

time_interval = [4, 6, 12]

I want to sum up the numbers like [4, 4+6, 4+6+12] in order to get the list t = [4, 10, 22].

Answer 1

Somewhat hacky, but seems to work:

def cumulative_sum(l):
  y = [0]
  def inc(n):
    y[0] += n
    return y[0]
  return [inc(x) for x in l]

I did think that the inner function would be able to modify the y declared in the outer lexical scope, but that didn't work, so we play some nasty hacks with structure modification instead. It is probably more elegant to use a generator.