How to return multiple values from one function to another in Python?

Question

I'm creating a program that checks if credit card numbers are valid. I'll post a picture of exactly what the instructions are so you have a better understanding of what I'm going for here. The instructions show that he's asked us to create two functions to calculate the sum for the odd numbers. so far I have this:

def main():
cardNum=int(input("Enter credit card number as a long integer: "))
singleDigit=getDigit(cardNum)
evenNum=sumOfDoubleEvenPlace(cardNum,singleDigit)
oddNum=sumOfOddPlace(cardNum)
print(evenNum)
print(oddNum)
checker=isValid(cardNum,sumOfDoubleEvenPlace,sumOfOddPlace)
if checker==True:
    print(cardNum,"is valid")
else:
    print(cardNum,"is invalid")


def isValid(cardNum:int,sumOfDoubleEvenPlace:int,sumOfOddPlace:int):
    checker=False
    singleDigit=getDigit(cardNum)
    evenNum=sumOfDoubleEvenPlace(cardNum,singleDigit)
    oddNum=sumOfOddPlace(cardNum)
    if (oddNum+evenNum)%10==0:
        checker=True
    else:
        checker=False
    return checker



def getDigit(cardNum:int)->int:
        for ch in str(cardNum)[0::2]:
            if 2*int(ch)<10:
                singleDigit=2*int(ch)
            else:
                singleDigit=((2*int(ch))%10)+((2*int(ch))//10)
            return singleDigit


def sumOfDoubleEvenPlace (cardNum:int,singleDigit:int)->int:
        evenNum=0
        i=0
        while i<(len(str(cardNum))//2):
            evenNum+=singleDigit
            i+=1
        return evenNum


def sumOfOddPlace(cardNum:int)->int:
    oddNum=0
    for ch in str(cardNum)[1::2]:
        oddNum+=int(ch)
    return oddNum

if __name__=="__main__":
    main()

I'm stuck on the functions getDigit() and sumOfDoubleEvenPlace(). I don't know how to convert the doubled number into a single digit in getDigit() and send them to sumOfDoubleEvenPlace() one at a time to be summed.

I understand that this can easily be completed in one function but that's not what my teacher wants :/

:::::UPDATE::::: I got a better understanding of what the two functions do from my teacher. I updated my code but now I'm running into global/local variable issues as the two functions reference each other.

I changed getDigit() and sumOfDoubleEvenPlace() to the following:

def getDigit(cardNum:int)->int:
doubleDigit=sumOfDoubleEvenPlace (cardNum)
if doubleDigit<10:
    singleDigit=doubleDigit
else:
    singleDigit=(doubleDigit%10)+(doubleDigit//10)

def sumOfDoubleEvenPlace (cardNum:int)->int:
evenNum=0
doubleDigit=0
singleDigit=getDigit(doubleDigit)
for ch in str(cardNum)[0::2]:
    doubleDigit=2*int(ch)
    getDigit(doubleDigit)
    evenNum+=singleDigit
return evenNum

What is "convert the doubled number into a single digit'? ex? — Saurav Sahu
– Saurav Sahu, Commented Oct 25, 2018 at 3:44
getDigit() has a return inside a for loop. That loop will only loop once. — John Gordon
– John Gordon, Commented Oct 25, 2018 at 3:57
I think it will be very beneficial if you add an example input, what you want to happen for that input and the expected output with examples. — BernardL
– BernardL, Commented Oct 25, 2018 at 4:08
You all have valid questions. I forgot to post a pic of the instructions, hope that clears it up — racedavid
– racedavid, Commented Oct 25, 2018 at 4:13

Henry Yik · Accepted Answer · 2018-10-25 04:54:11Z

1

You are cross linking multiple functions which makes it quite hard to comprehend. I will try to make it more straightforward.

Step 1 & 2: Double every second digit and get sum.

def step_one_and_two(number):
    result = 0
    for i in number[0::2]: # get all double digits
        num = int(i)*2
        if num <10:
            result += num
        else:
            result += num-10+1 #Add up the two digits to get single digit num
    return result

Step 3:

def step_three(number):
    result = 0
    for i in number[1::2]: #get odd place digits
        result += int(i)
    return result

Result:

first_card = "4388576018402626"
second_card = "4388576018410707"

print (step_one_and_two(first_card), step_three(first_card))
print (step_one_and_two(second_card),step_three(second_card))

37 38
29 41

answered Oct 25, 2018 at 4:54

Henry Yik

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