Sum of Digits in an Integer?

Question

I'm working on an assignment in Python and don't understand the problem with my code.

Based on other answers on Stack Overflow, the answer seems to be:

def digit_sum(number):

    return (sum(int(digit) for digit in str(number)))

Where as my code (below) is not working. Why not?

def digit_sum(number):
    for digit in str(number): 
        return sum(int(digit))

Answer 1

You broke the for loop with a return before the loop finishes. You need to store the accumulative sum and then return it after the loop finishes.

Also, you need to understand what is a 'Single line for loop' in Python. Let's see what does the return mean in your first block of code:

(sum(int(digit) for digit in str(number)))

We can turn this line into multiple steps:

1 Get an array of digits as String

This step can be done like this

def get_digits_as_string(num):
    return [digit for digit in str(num)]

Running above function you can see

>>> get_digits_as_string(12345)
['1', '2', '3', '4', '5']

2 Convert the array of string into an array of integers(also in one line)

We just type cast single string element in the array into int

def get_digits_as_int(num):
    return [int(digit) for digit in str(num)]

if you run it you will get:

>>> get_digits_as_int(12345)
[1, 2, 3, 4, 5]

3 Sum the array of int

This is equivalent to your first block of code

def digit_sum(num):
    return sum([int(digit) for digit in str(num)])

Here is a post that is helpful if you want to know more about Single Line for Loops: https://blog.teamtreehouse.com/python-single-line-loops

Hope my answer helps.

Answer 2

Your code doesn't work because you are returning too early.

The return keyword takes whatever you give it and returns it to the caller of the function.

In the first iteration of the for loop, you calculating the sum of the first digit and then returning it.

EG: Number is 1234

so the for loop is iterating over "1234"

So the first digit of "1234" is "1"

Then you take the sum of 1 (whatever that means lol)

And so you would return the number 1