calling func. change the input [closed]

Answer 1

This is basicly the same, but it does not change the value of numbers.

def rec_cumsum(numbers):
    if len(numbers) == 0 : return numbers
    if len(numbers) == 1 : return numbers
    return [numbers[0]] + rec_cumsum([numbers[0]+numbers[1]] + numbers[2:])

Answer 2

Use a second list:

def rec_cumsum(numbers):
    if len(numbers) == 0: return []
    sums = [ numbers[0] ]
    for i in range(1, len(numbers)):
        sums.append(sums[i-1] + numbers[i])
    return sums