freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-python/69b1028d6e265413d0198a2a.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
69b1028d6e265413d0198a2a	Challenge 231: ISBN-10 Validator	29	challenge-231

--description--

Given a string, determine if it's a valid ISBN-10.

An ISBN-10 consists of hyphens ("-") and 10 other characters. After removing the hyphens ("-"):

• The first 9 characters must be digits, and
• The final character may be a digit or the letter "X", which represents the number 10.

To validate it:

• Multiply each digit (or value) by its position (multiply the first digit by 1, the second by 2, and so on).
• Add all the results together.
• If the total is divisible by 11, it's valid.

--hints--

is_valid_isbn10("0-306-40615-2") should return True.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_isbn10("0-306-40615-2"), True)`)
}})

is_valid_isbn10("0-306-40615-1") should return False.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_isbn10("0-306-40615-1"), False)`)
}})

is_valid_isbn10("0-8044-2957-X") should return True.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_isbn10("0-8044-2957-X"), True)`)
}})

is_valid_isbn10("X-306-40615-2") should return False.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_isbn10("X-306-40615-2"), False)`)
}})

is_valid_isbn10("0-6822-2589-4") should return True.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_isbn10("0-6822-2589-4"), True)`)
}})

--seed--

--seed-contents--

def is_valid_isbn10(s):

    return s

--solutions--

def is_valid_isbn10(s):
    isbn = s.replace("-", "")

    if len(isbn) != 10:
        return False

    total = 0

    for i in range(9):
        if not isbn[i].isdigit():
            return False
        total += int(isbn[i]) * (i + 1)

    last = isbn[9]

    if last == "X":
        total += 10 * 10
    elif last.isdigit():
        total += int(last) * 10
    else:
        return False

    return total % 11 == 0