python - How to write a function that adds numbers in a list by calling itself? -

i'm trying write function adds numbers in list calling in python. here's example of mean:

def factorial(n):    if n == 1:       return 1    else:       return n * factorial(n-1) 

how use find sum of list?

nums = [1, 3, 2, 8, 9] def rec_sum(nums):     if not nums: return 0     return nums[0] + rec_sum(nums[1:])  >>> rec_sum(nums) 23 

you in 1 line:

def rec_sum(nums):     return nums[0] + rec_sum(nums[1:]) if nums else 0 

to avoid shallow copies of list being made nums[1:] on each call can more efficient:

def rec_sum(nums, i=0):     if >= len(nums): return 0     return nums[i] + rec_sum(nums, i+1) 

it's fun use y-combinator

>>> y = lambda f: (lambda x: x(x))(lambda y: f(lambda *args: y(y)(*args))) >>> rec_sum = lambda f: lambda nums: nums[0] + f(nums[1:]) if nums else 0 >>> y(rec_sum)(nums) 23