遍历一段代码时收到“ TypeError：字符串索引必须为整数”

Question

I am taking an input with

CC = (input("What is your credit card number?"))

When I take the sum of every other digit, starting from the first, I use this code (which works):

amex_sum = sum(int(i) for i in CC[::2])

However, when I try to take the sum of every other digit, starting from the second digit and until the 16th digit, with the following code

MC_sum = sum(int(i) for i in CC[1,15,2])

I receive the error: "TypeError: string indices must be integers."

Why does one iteration work and not the other? Isn't the code essentially the same?

Answer 1

You're slicing it incorrectly, you are doing CC[1,15,2] but this creates a tuple (1, 15, 2) to be indexed in CC This wont work of course as CC is a string and takes only integer indices.

What you want is CC[1:15:2] to slice from the second index to the sixteenth with a step of two.