Hi,
During a review, the person ask me if his code check if the X character is only acceptable at the end of the ISBN. So I look at the test and I see this test:
def test_x_is_only_valid_as_a_check_digit(self):
self.assertIs(is_valid("3-598-2X507-9"), False)I think this is the test that test it. But here is the problem I have.
The sum % 11 is not equal to 0.
Here is his solution:
def is_valid(isbn):
isbn = isbn.replace('-', '')
if len(isbn) != 10:
return False
sum = 0
for index, digit in enumerate(list(isbn)):
if digit.isdecimal():
sum += int(digit) * (10 - index)
elif digit == 'X':
sum += 10
else:
return False
return sum % 11 == 0 Here the operation his code is doing:
3 * 10 + 5 * 9 + 9 * 8 + 8 * 7 + 2 * 6 + 10 + 5 * 4 + 0 * 3 + 7 * 2 + 9 * 1 = 268
268 % 11 = 4
As you can see the 10 (replacing the X value) is not multiplied (this is how he write his solution). Because of this his test pass but not for the good reason. It pass because the sum % 11 != 0 and not because X is valid only as a check character.
I think we should add the test case where the ISBN is "3-598-2X507-5". This is a case where the sum is 264 (and 264 % 11 == 0). Doing so will handle that sum % 11 == 0 and the X character is not at the end.
Hi,
During a review, the person ask me if his code check if the
Xcharacter is only acceptable at the end of the ISBN. So I look at the test and I see this test:I think this is the test that test it. But here is the problem I have.
The sum % 11 is not equal to 0.
Here is his solution:
Here the operation his code is doing:
As you can see the
10(replacing theXvalue) is not multiplied (this is how he write his solution). Because of this his test pass but not for the good reason. It pass because thesum % 11 != 0and not becauseXis valid only as a check character.I think we should add the test case where the ISBN is
"3-598-2X507-5". This is a case where the sum is264(and264 % 11 == 0). Doing so will handle thatsum % 11 == 0and theXcharacter is not at the end.