freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-python/6a0dcd03ee4e68698080ef6c.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
6a0dcd03ee4e68698080ef6c	Challenge 308: Credit Card Validator	29	challenge-308

--description--

Given a string of digits for a credit card number, determine if it's a valid card number using the following method:

• Starting from the second-to-last digit, double every other digit moving left.
• If doubling a digit results in a number greater than 9, subtract 9.
• Sum all the digits (doubled and undoubled).
• If the total is divisible by 10, the number is valid.

--hints--

is_valid_card("4532015112830366") should return True.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_card("4532015112830366"), True)`)
}})

is_valid_card("5425233430109903") should return True.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_card("5425233430109903"), True)`)
}})

is_valid_card("371449635398431") should return True.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_card("371449635398431"), True)`)
}})

is_valid_card("6011111111111117") should return True.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_card("6011111111111117"), True)`)
}})

is_valid_card("4532015112830367") should return False.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_card("4532015112830367"), False)`)
}})

is_valid_card("1234567890123456") should return False.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_card("1234567890123456"), False)`)
}})

is_valid_card("4532015112830368") should return False.

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(is_valid_card("4532015112830368"), False)`)
}})

--seed--

--seed-contents--

def is_valid_card(number):

    return number

--solutions--

def is_valid_card(number):
    total = 0
    for i, digit in enumerate(reversed(number)):
        d = int(digit)
        if i % 2 == 1:
            d *= 2
            if d > 9:
                d -= 9
        total += d
    return total % 10 == 0