I apologize for the poor explanation.
I added the description of what they call a more challenging way to complete the task:
If you’re looking for a challenge, try this: to get the rightmost digit of a number, you can modulo (%) the number by 10. To remove the rightmost digit you can floor divide (//) the number by 10. (Don’t worry if you’re not familiar with floor division—you can look up the documentation here. Remember, this is a challenge!)
I’m trying to figure out how to do this. Right now I’m sitting with something like this
l = len(str(n))
list1 = 
c = 0
for n in range(l-1):
x = n // 10**(c)
x = n % 10**(c+1)
c += 1
I receive the following error message:
Your function fails on digit_sum(434). It returns 1 when it should return 11.