Adding elements in a list in Python

Question

I have a list a=[1,2,3,4,5,6]

I would like to create a function that sums every n elements together in a new list for example

my_sum(a,2)=[3,7,11] - a new list with a[0]+a[1], a[2]+a[3]

my_sum(a,3)=[6,15] - a[0]+a[1]+a[2],

I am stuck, anyone got an idea?

Answer 1

Try this:

def my_sum(a, n):
    return [sum(a[i: i + n]) if len(a[i: i + n]) >= n else None for i in range(0, len(a), n)]
a=[1,2,3,4,5,6]
my_sum(a, 4)

Answer 2

Perhaps this is what you're looking for, also quite readable:

def my_sum(array, n):
    result = []
    if n > len(array):
        return []
    for i in range(0, len(array), n):
        result.append(sum(array[i:i+n]))

    return result

ls = [1,2,3,4,5,6]
print(my_sum(ls, 5))

Answer 3

You can try this:

def my_sum(a, b):
    sum = 0
    new_list = []
    lenght = len(a)
    if lenght % b == 0:
        for count, value in enumerate(a):
            if count + 1 == lenght:
                sum += value
                new_list.append(sum)
            elif count != 0 and count % b == 0:
                new_list.append(sum)
                sum = 0
                sum += value
            else:
                sum += value
        return new_list
    else:
        print("It's not possible")
        return

You can do this only If the number of the sum is divisible by the list lenght (this is the reason for the first "If").