Perl is great, its just too tough for me. Python is more clear. I need your help

Sorry, what part of "I don't do snakes" isn't clear?

I want to understand this.

Not that hard given the split that proceeds the code you quoted. Iterate over each element of the array and find the ordinal of the character in that element. Add the integer value of that ordinal to the previous value and perform a modulo arithmetic operation on the sum and store the sum back into the original scalar.