For ISBN13 calculate and validate, when the checksum is 0 returned value is X instead

[mohsenBanan]

bookUtils.cs -i isbnCalculate13 978-1-960957-03
Returns X --- instead of 0

bookUtils.cs -i isbnValidate13 978-1-960957-03-X --- Returns True
bookUtils.cs -i isbnValidate13 978-1-960957-03-0 --- Returns False

978-1-960957-03-0 is a valid ISBN13.

Returning X instead of 0 seems to be by design, but why?

If it is not by design, then it is a bug.

P.S. bookUtils.cs is just a python command service that uses checkdigit.isbn

[harens]

Hey @mohsenBanan 👋

Thanks for using checkdigit and for opening this issue! You're completely right that this is a bug (ISBN-13 shouldn't produce X as a check digit). I've pushed a commit that should fix this and I'll publish a new release shortly.

Thanks again for the bug report and for using checkdigit.

[harens]

@all-contributors please add @mohsenBanan for bug.

[allcontributors]

@harens

I've put up a pull request to add @mohsenBanan! 🎉