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

a = [1, 2, 3 ,4, 5]

# Using list comprehention
cumsum = [sum(a[:i+1]) for i in range(len(a))]           # [1, 3, 6, 10, 15]

# Using map()
cumsum = map(lambda i:  sum(a[:i+1]), range(len(a)))     # [1, 3, 6, 10, 15]