Thanks,
But in our case, the second iterable is less in length than the first. Unlike your example. How would you explain that?

your index value is sometimes greater than abc_lower and abc_upper 's length of 26 (i.e., index >=26)

you need to figure out a way to make values greater than 26 correspond to the same value within 26

e.g. 26=>0, 28=>2, etc.

1. map(int, str(number)) returns a list of all the digits in a number. e.g,

list(map(int,str(123))) = [1,2,3]

2. when there are more than one iterables in the map function, the given function iterates through both lists, kinda like zip. a takes the values of the first iterable and b takes the value of the second. e.g.,

list(map(lambda a, b: a+b, [1,2,3], [4,5,6])) = [1+4, 2+5, 3+6] = [5,7,9]