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Python Python Basics (Retired) Putting the "Fun" Back in "Function" Functions

functions challenge - stuck on first task

I can't really think of another way to word the code to receive the correct sum. I was able to somehow pass the first task with another code, but I was receiving an incorrect sum.

The error: list index out of range.

# add_list([1, 2, 3]) should return 6
# summarize([1, 2, 3]) should return "The sum of [1, 2, 3] is 6."
# Note: both functions will only take *one* argument each.
def add_list(list):

    total = 0

    for i in list:
        total += list[i]

    return total 

2 Answers

14,630 Points

Hi Alec, the function was correctly set, but you are calling list[i] within the loop, which is wrong.

  • first loop pass, i = 1, so list[1] gets called - total becomes 2
  • second pass, i = 2, so list[2] gets called - total becomes 5
  • third pass, i =3 , so list[3] gets called which is 'out of index' as there are only 3 elements in the list.

So, what you need is just 'i' to be added to total, not list[i]

good luck!

Kenneth Love
Kenneth Love
Treehouse Guest Teacher

You don't need list[i] when you do for i in list:. i is the current item for this step in the list. Look at this:

my_list = ['a', 'b', 'c']

for letter in my_list:

This would print


because each time the loop loops, letter is changed to the next item in my_list.

Thank you for explaining it in such a simple way there. It makes a lot of sense!