Checking if an ISBN number is correct

Question

I\'m given some ISBN numbers e.g. 3-528-03851 (not valid) , 3-528-16419-0 (valid). I\'m supposed to write a program which tests if the ISBN number

Answer 1

Your code is nice -- well done for writing idiomatic Python! Here are some minor things:

---

When you see the idiom

result = 
for elt in :
    result += elt

you can replace it by a list comprehension. In this case:

result = sum((i+1)*int(digit) for i, digit in enumerate(digits)

or even more concisely:

return sum((i+1)*int(digit) for i, digit in enumerate(digits) % 11 == check_digit

Of course, it is a value judgement whether this is better than the original. I would personally consider the second of these to be best.

Also, the extra parentheses in (result % 11) == check_digit are extraneous and I don't really think you need them for clarity. That leaves you overall with:

def validate(isbn):
    check_digit = int(isbn[-1])
    match = re.search(r'(\d)-(\d{3})-(\d{5})', isbn[:-1])

    if match:
        digits = match.group(1) + match.group(2) + match.group(3)
        parity = sum((i+1)*int(digit) for i, digit in enumerate(digits)
        return parity % 11 == check_digit
    else:
        return False

Note that you do still need the return False to catch the case that the ISBN is not even in the right format.