Write a function credit(n, mode) that takes as input an integer n and an optional string argument mode. You can assume without checking that n is an integer and mode is a valid string (if provided). The function is intended to help with the validation and generation of 16-digit credit card numbers. The first 15 digits of a typical credit card number identify the institution that issued the card and the individual account, and the final (right-most) digit is a check digit.

The validation of a credit card number, explained at an example, goes as follows:

• Take, for example, the 16-digit credit card number 4578423013769219.
• The check digit is the final 9 and we first process the first 15 digits 4-5-7-8-4-2-3-0-1-3-7-6-9-2-1.
• Starting with the first digit, we multiply every second digit by two, resulting in 8-5-14-8-8-2-6-0-2-3-14-6-18-2-2.
• Every time we have a two-digit number, we add those digits together for a one-digit result: 8-5-5-8-8-2-6-0-2-3-5-6-9-2-2.
• We add up all the numbers: 8 + 5 + 5 + 8 + 8 + 2 + 6 + 0 + 2 + 3 + 5 + 6 + 9 + 2 + 2 = 71.
• The credit card number is valid if and only if the computed sum plus the check digit is divisible by 10. In our example, 71 + 9 = 80 is divisible by 10. Hence this is a valid credit card number.

The function credit can do two things depending on the value of mode.

• If mode has the string value verify, the function checks whether n corresponds to a valid credit card number by verifying that the check digit is correct, using the algorithm explained above. The function then returns the Boolean value True if the integer ncorresponds to a valid credit card number, and otherwise False.

• If mode has the string value calculate, n should be a positive 15-digit integer and the function returns the single check digit as an integer. If n is not a positive 15-digit integer, then the function should return None.

• If mode is not specified, the value verify should be assumed by default.

Answer rating: 100% (QA)

Rawcode def creditn modeverify if n is negative or not a 16 digit number if n 0 or lenstrn 16 return ... View the full answer