How to iterate through values of a dictionary until there is no more values (reached the end of the dictionary)?

Let’s say I have a dictionary such as

d = {'Item 1': [3,4,5,3], 'Item 2': [2,3,4], 'Item 3': [5,34,75,35,65]}

What I want to do is calculate the summation of two elements in the list and add them to a total. Such as for Item 1, I would want to do 3 + 4, 4 + 5, 5 + 3, and stop once I have reached the last value of the dictionary. Similarly, I want to do this with all the values in the dictionary and add them to a grand total.

>Solution :

If you have Python 3.10, you can use itertools.pairwise:

from itertools import pairwise, chain

d = {
    'Item 1': [3,4,5,3],
    'Item 2': [2,3,4],
    'Item 3': [5,34,75,35,65]
}

for key, numbers in d.items():
    s = sum(chain.from_iterable(pairwise(numbers)))
    print(f"{key}: {s}")

Output:

Item 1: 24
Item 2: 12
Item 3: 358

Alternatively, if you don’t have Python 3.10, you can define your own pairwise:

from itertools import tee, chain

def pairwise(iterable):
    a, b = tee(iterable)
    next(b, None)
    yield from zip(a, b)

If you just want a total sum:

total_sum = sum(sum(chain.from_iterable(pairwise(nums))) for nums in d.values())