Simple expression for a cumulative sum over list

Question

I have a Python array, and I want to write a single expression that returns an array with sum of all previous numbers. For example we have:

arr1 = [1,2,3,4]

And my function should return :

[1, 3, 6, 10]

I know that it's possible to make it with simple loop or even recursivly, but is it possible to make in one line? Something like:

def converter(arr):
    arr1 = [x + y for x,y in arr ]
    return arr1

Answer 1

Since Python 3.2, you can use itertools.accumulate:

>>> from itertools import accumulate
>>> arr = [1,2,3,4]
>>> list(accumulate(arr))
[1, 3, 6, 10]