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# 6.29 (Financial: credit card number validation) Credit card numbers follow certain
# patterns: It must have between 13 and 16 digits, and the number must start with:
# ■ 4 for Visa cards
# ■ 5 for MasterCard credit cards
# ■ 37 for American Express cards
# ■ 6 for Discover cards
# In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card numbers.
# The algorithm is useful to determine whether a card number is entered correctly
# or whether a credit card is scanned correctly by a scanner. Credit card
# numbers are generated following this validity check, commonly known as the
# Luhn check or the Mod 10 check, which can be described as follows (for illustration,
# consider the card number 4388576018402626):
# Return True if the card number is valid
def isValid(number):
if getSize(number) >= 13 and getSize(number) <= 16:
if prefixMatched(number, 4) or prefixMatched(number, 5) or \
prefixMatched(number, 6) or getPrefix(number, 2) == 37:
return True if (sumOfDoubleEvenPlace(number) +
sumOfOddPlace(number)) % 10 == 0 else False
def sumOfDoubleEvenPlace(number):
numberList = []
oddPlaceNumberList = []
for i in range(len(list(str(number)))):
numberList.append(int(list(str(number))[i]))
numberList.reverse()
for j in range(1, len(numberList), 2):
oddPlaceNumberList.append(numberList[j])
doubleOddPlaceNumber = [i * 2 for i in oddPlaceNumberList]
digitOddPlaceNumber = [getDigit(i) for i in doubleOddPlaceNumber]
return sum(digitOddPlaceNumber)
# Return this number if it is a digit, otherwise, return
# the sum of the digits
def getDigit(number):
numberList = []
for i in range(len(list(str(number)))):
numberList.append(int(list(str(number))[i]))
return sum(numberList)
# Return sum of odd place digits in number
def sumOfOddPlace(number):
numberList = []
totalNumber = 0
for i in range(len(list(str(number)))):
numberList.append(int(list(str(number))[i]))
numberList.reverse()
for j in range(0, len(numberList), 2):
totalNumber += numberList[j]
return totalNumber
# Return true if the digit d is a prefix for number
def prefixMatched(number, d):
return True if int(str(number)[0]) == d else False
# Return the number of digits in d
def getSize(number):
return len(str(number))
# Return the first k number of digits from number. If the
# number of digits in number is less than k, return number
def getPrefix(number, k):
if len(str(number)) <= k:
return number
else:
return int(str(number)[0:k])
def main():
num = eval(input("Enter credit card number: "))
print(isValid(num))
main()
