Problem Set 8: Book Identifier

Task Outline

• Due Date: Monday, November 11, 2019
• Total Points: 10
• Implement a Python program that validates ISBN-10 numbers.

Background Theory

• Any book that you purchase has an International Standard Book Number, otherwise known as an ISBN or ISBN-10. This is a 10-digit number that uniquely identifies books and media products published internationally.
• It turns out that the last number of an ISBN-10's digits is a check digit, otherwise known as a checksum, which is a number related mathematically to its preceding digits.
• The digits of an ISBN-10 are supposed to adhere to a formula, and this check digit allows you to verify whether an ISBN-10's other nine digits are valid, without having to resort to other means of verification, for instance, by performing a query on a database of books.

Calculating the Check Digit

• The check digit of an ISBN-10 number can be defined as follows. If $x_1$ represents an ISBN-10's first digit, and $x_{10}$ represents its last digit, then we have the following:

• In other words, to compute an ISBN-10's tenth digit, multiply its first digit by 1, its second digit by 2, its third digit by 3, its fourth digit by 4, its fifth digit by 5, its sixth digit by 6, its seventh digit by 7, its eighth digit by 8, and its ninth digit by 9. Take the sum of those products and perform a modulus with 11. The result should be the ISBN-10's tenth digit.

Example Case

• For example, the ISBN-10 for the textbook Absolute Beginner's Guide to C, is 0-789-75198-4, the tenth digit of which is 4. Let's take the sum of the products of theISBN-10's first nine digits:

• If we now compute 290 modulus 11, we get a result of 4, which is equal to the tenth digit in the ISBN-10. This verifies that the ISBN-10 number is legitimate.

Hints

• Note that the ISBN-10 is being read in as a string, and it gets converted to an integer by using the int() function. The reason for this procedure is to accommodate ISBN-10's with leading zeros.
• Now that we have an ISBN-10 in integer form, how can we get at its tenth(i.e. rightmost) digit? Perhaps we can make a clever use of the modulus operator:

tenth = isbncode % 10

• Now, how can we get a that same variable's ninth digit? Perhaps we can get rid of its tenth digit by using integer division:

isbncode = isbncode // 10

• Afterwards, we can access the ninth digit by using the modulus operator:

ninth = isbncode % 10

• Hopefully, you can detect a pattern here. Remember that a certain looping construct such as the for loop can be very useful here.

Code Distribution

Contents of pset08.zip:

PSet08BookIdentifier/
├── bookidentifier.py
└── testbookidentifier.py

Specification

• Write a Python program in the file bookidentifier.py that determines whether an ISBN-10 number is legitimate or not.
• You will write your solution in a function called validatebook(isbncode) right below the place where it says: YOUR CODE HERE
• If the ISBN-10 number is valid, then your validatebook method should return the string YES. Otherwise, if the ISBN-10 number is not valid, then your validatebook method should return the string NO.
• When the function call validatebook("0789751984") is executed, the output of the program should be: YES

Testing

• Run the file testbookidentifier.py to execute the PyUnit test bench. PyUnit indicates a successful test with an OK output, and an unsuccessful test with a FAIL output.

Submission

• Upload the file bookidentifier.py to the Web-CAT automated grading platform.