Python | Give list [1,2,3,4] -> return 1*2+2*3+3*4

So as i said in the title, i want to multipy each two neigbors in the list and sum them all – with a single code line.

I’m looking for the most elegant and efficient method, without using extra memory or such.

Here’s what I do have now:

import numpy as np
G = lambda array: sum(np.multiply(array[:-1], array[1:])))

That works, but when i write array[:-1] and array[1:], doesn’t it create two new arrays? If so, is there a way to do that with the same original array?

Or maybe you can come up with a nicer way to do that 🙂

>Solution :

Try the following:

    lst = [1,2,3,4]
    func = lambda lst: sum([lst[i]*lst[i+1] for i in range(len(lst)-1)])
    func(lst)