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

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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

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.