Tell us what’s happening:
Hello, I am getting an error when it comes to getting the “Valid ISBN Code.” right. When running print(validate_isbn(1530051126,10)), I get “Invalid ISBN Code.” followed by a line saying “None”. I believe the None is making the error but I’ve looked up and down the code.
Your code so far
import re
def validate_isbn(isbn, length):
if len(str(isbn)) != length:
print(f'ISBN-{length} code should be {length} digits long.')
return
main_digits = str(isbn)[0:length]
given_check_digit = str(isbn)[-1]
main_digits_list = [int(digit) for digit in main_digits]
# Calculate the check digit from other digits
if length == 10:
expected_check_digit = calculate_check_digit_10(main_digits_list)
else:
expected_check_digit = calculate_check_digit_13(main_digits_list)
# Check if the given check digit matches with the calculated check digit
if given_check_digit == expected_check_digit:
print('Valid ISBN Code.')
else:
print('Invalid ISBN Code.')
def calculate_check_digit_10(main_digits_list):
# Note: You don't have to fully understand the logic in this function.
digits_sum = 0
# Multiply each of the first 9 digits by its corresponding weight (10 to 2) and sum up the results
for index, digit in enumerate(main_digits_list):
digits_sum += digit * (10 - index)
# Find the remainder of dividing the sum by 11, then subtract it from 11
result = 11 - digits_sum % 11
# The calculation result can range from 1 to 11.
# If the result is 11, use 0.
# If the result is 10, use upper case X.
# Use the value as it is for other numbers.
if result == 11:
expected_check_digit = '0'
elif result == 10:
expected_check_digit = 'X'
else:
expected_check_digit = str(result)
return expected_check_digit
def calculate_check_digit_13(main_digits_list):
# Note: You don't have to fully understand the logic in this function.
digits_sum = 0
# Multiply each of the first 12 digits by 1 and 3 alternately (starting with 1), and sum up the results
for index, digit in enumerate(main_digits_list):
if index % 2 == 0:
digits_sum += digit * 1
else:
digits_sum += digit * 3
# Find the remainder of dividing the sum by 10, then subtract it from 10
result = 10 - digits_sum % 10
# The calculation result can range from 1 to 10.
# If the result is 10, use 0.
# Use the value as it is for other numbers.
if result == 10:
expected_check_digit = '0'
else:
expected_check_digit = str(result)
return expected_check_digit
def main():
user_input = input('Enter ISBN and length: ')
try:
values = user_input.split(',')
isbn = values[0]
length = int(values[1])
if not re.fullmatch('\d+',isbn):
print('Invalid character was found.')
if length == 10 or length == 13:
validate_isbn(isbn, length)
else:
print('Length should be 10 or 13.')
except IndexError:
print('Enter comma-separated values.')
except ValueError:
print('Length must be a number.')
# main()
print(validate_isbn(1530051126,10))
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Challenge Information:
Debug an ISBN Validator - Debug an ISBN Validator