(Business: check ISBN-10)

Question

An ISBN-10 (International Standard Book Number) consists of 10 digits: d1d2d3d4d5d6d7d8d9d10. The last digit, d10, is a checksum, which is calculated from the other nine digits using the following formula:

(d1 * 1 + d2 * 2 + d3 * 3 + d4 * 4 + d5 * 5 + d6 * 6 + d7 * 7 + d8 * 8 + d9 * 9) % 11

If the checksum is 10, the last digit is denoted as X according to the ISBN-10 convention. Write a program that prompts the user to enter the first 9 digits and displays the 10-digit ISBN (including leading zeros).

Sample Run 1

Enter the first 9 digits of an ISBN as a string: 3601267

Incorrect input. It must have exact 9 digits

Sample Run 2

Enter the first 9 digits of an ISBN as a string: 013601267

The ISBN-10 number is 0136012671

Sample Run 3

Enter the first 9 digits of an ISBN as a string: 013031997

The ISBN-10 number is 013031997X

Answer 1

def generate_isbn():

"""

prompts user for the first 9 digits of an ISBN10 code,

calculates checksum

returns the ISBN10 as a string

"""

user_input = input('enter the first 9 digits of an ISBN as a string: ')

if len(user_input) != 9:

return 'Incorrect input. It must have exact 9 digits'

#we're going to assume the user input a string of integers

#feed the string into a list

digits = [int(i) for i in user_input]

#calculate checksum according to rule provided

sum_products = 0

for i in range(9):

#digits[0] needs to be multiplied by 1, etc.

sum_products += digits[i] * (i + 1)

checksum = sum_products%11

#add checksum character to digits list, applying the special rule for 'X'

checksum_character = 'X' if checksum == 10 else checksum

digits.append(checksum_character)

#convert each digit to a str, and concatentate before returning

return ''.join([str(i) for i in digits])