Question: PYTHON Check Digits Check digits are used to validate a value, whether its a Vehicle Identification Number (VIN), ISBN # used for books. The basic

**PYTHON**

Check Digits

Check digits are used to validate a value, whether its a Vehicle Identification Number (VIN), ISBN # used for books. The basic idea is that digit in a string is used to validate the other characters in the string. If one of the characters is entered incorrectly or transposed, then the calculated digit will not match the entered digit, and we can warn the user that the value is incorrect.

We are creating a check digit scheme for making unique assignment numbers for classes. The assignment number will be 13 characters in length. The last character is will be the check digit. The valid digits that can be used in our scheme are [0-9] and [A-F]. We wont need a check digit to know the entry is invalid if its not 13 characters or uses a digit other than given.

Calculating the Check Digit

Each character has a numeric value. If the character is [0-9] then it has the corresponding value. A zero has a value of 0, a 1 has a value 1, and so on. A has a numeric value 10, B has a numeric value 11, C has a numeric value 12, etc on up to F which has a value of 15. We multiply each value by the weight of its position, and sum up the values. Lets do an example, lets say our assignment is BAF189D234EA2.

Character	B	A	F	1	8	9	D	2	3	4	E	A	2
Value	11	10	15	1	8	9	13	2	3	4	14	10
Weight	0	1	2	3	4	5	6	7	8	9	10	11	0
Product	0	10	30	3	32	45	78	14	24	36	140	110

The sum of the product is 522. To calculate the result we use modulus 10 on the result. 522 mod 10 is 2, which is our check digit above. If the assignment was entered as BAF189D234EA5, then the calculated checkdigit 2 does not match the check digit 5 as given. So we know the user entered an invalid value.

Class and assignment Type

The first character ( not index ), tells us what class the assignment is for. The only valid values for the first character is A, B, C, or D

First character in string	Class
A	CS101
B	CS191
C	CS201
D	CS291

Also, the second character lets us know the assignment type. The only valid value for the second character is A, B, C, D, or E.

Second character in string	Class
A	Test
B	Program
C	Quiz
D	Final
E	Other

Requirements

Validate the input is valid ( must be 13 characters, valid characters for all characters and limited further for character 1 and 2.

Once the user enters an empty string the program will end.

Development notes.

Using .upper() will change all the characters to the given case. Making comparisons easier. It is ok for the user to enter it in lower case. We will upper case the value for them.

Break the program down into meaningful functions. Try to solve one problem at a time.

Test Values to help in your testing

Value	Result
ABC	Incorrect, the value has to be 13 characters in length
BAF189D23ZEA2	Incorrect, there is an illegal character Z in the value
FAF189D234EA2	Incorrect, the first character cannot be F, only A-D
B8F189D234EA2	Incorrect, the second character cannot be 8, only A-E
BAF189D234EA2	Valid, class is CS191 and assignment is a Test
DE2017F000018	Valid, class is CS291 and the assignment is Other
AD1702FAC1990	Valid, class is CS101 and the assignment is a Final

Example

Python 3.7.0 (v3.7.0:1bf9cc5093, Jun 27 2018, 04:06:47) [MSC v.1914 32 bit (Intel)] on win32

Type "copyright", "credits" or "license()" for more information.

>>>

RESTART: C:\Users\kbingham\Documents\PythonProjects\CS101\Programming\Ideas\CheckDigits\AssignmentCheckDigits.py