Elegant pythonic cumsum

Question

What would be an elegant and pythonic way to implement cumsum?
Alternatively - if there\'a already a built-in way to do it, that would be even better of course...

Answer 1

in place:

a=[1,2,3,4,5]
def cumsum(a):
    for i in range(1,len(a)):
        a[i]+=a[i-1]

cumsum(a)
print a
"[1, 3, 6, 10, 15]"