Why is function returning none instead of the value? (Python)

Question

I’m trying to make a blackjack game and I’m having issues with a recursive function returning none. I have a function to calculate the score of the hand and check if it’s over 21. If it is, it checks to see if there’s an 11 in the hand; if there is, another function gets called to change it to a 1 instead, then calls the function to calculate the score.

I’ve added a break point and it adds up just fine until it returns the total value back to the class variable

    def get_score(self, hand):
        total = 0
        for card in hand:
            total += card
        if total > 21:
            if 11 in hand:
                return self.ace_conversion(hand)
        else:
            return total
        
    def ace_conversion(self, hand):
            index = hand.index(11)
            hand[index] = 1
            self.get_score(hand)

On another post, someone recommended making both sides of the if statement return and that’s when I started having this issue. Previously, it was:

…
        if total > 21:
            if 11 in hand:
                self.ace_conversion(hand)
        else:
            return total

When I had this, it would calculate the correct value, then return the original value of the hand.

Asked By: Zach Reese

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Source

Answer 1

   if total > 21:
       if 11 in hand:
           return self.ace_conversion(hand)

There is nothing returned in this branch if there is no 11 in the hand.

Even if there is an 11, ace_conversion doesn’t ever return any value, so there’s nothing to return in that case either.

The fact that ace_conversion calls a function that returns a value doesn’t automatically cause a value to be returned from ace_conversion.

You need to explicitly include a return statement in ace_conversion and also make sure there is a return statement in the branch where total > 21 and there is no 11 in the hand.

Answered By: The Photon

Answer 2

The cases are not exhaustive, you need to cover the scenario where the hand is greater than 21 without an 11 in hand.

Solution:

def get_score(hand):
    total = sum(hand)
    if total > 21 and 11 in hand:
        index = hand.index(11)
        hand[index] = 1
        return get_score(hand)
    else:
        return total

Do note that though readable, this performs two linear scans on the hand.

Answered By: Ci Leong

Answer 3

When the ace_conversion(hand) function is finished, it does not return any value. Therefore, when self.ace_conversion(hand) is called, the get_score(hand) function does not return any value.

You can fix this by adding a return statement to ace_conversion(hand), which returns the score returned by self.get_score(hand).

Answered By: The Girl Programmer

Why is function returning none instead of the value? (Python)

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