What will be the output of code written below & why?

Question

What will be the output of below code?
a=[x for x in range(4)]
print(sum(a[1::-2]+a[:3])):

Answer 1

The first line is just a list comprehension used to turn the range object into a list object.

a[1::-2] is [1], as we start at index 1 and go back 2 steps until we are out of bounds, which happens on the first step we take.

a[:3] is just [0,1,2], hence the sum over all the elements in the lists is 4.