Answer 1

What you're doing here is called Parallel assignment.
It allows you to assign the values in an iterable to a list  (or tuple) of variables in a single and elegant statement. This means each item in the list is assigned to the variables respectively.

Since s[::-1] returns the reverse of the original list, we can say something like this
>>>a,b,c = [0,2,1]
Here, a = 0,b = 2, c = 1(parallel assignment)
So, s[a] means s[0] which is 1