Summarize needs to return a string, however it is currently returning a list. join the list with spaces to make it a string. also you need to convert the return value of add_list to a string as well (you did this on the line above for list_1, but the sum needs to be a string too):

# 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_1):
  sum = 0
  for item in list_1:
     sum = sum + item
  return sum

def summarize(list_1):
   sentence = "The sum of X is Y"
   word_list = sentence.split()
   word_list[3] = str(list_1)
   word_list[5] = str(add_list(list_1))
   return " ".join(word_list)

also dont call the function in the challenge, it does not ask you to do that

a simpler way would be to use .format which makes the whole function one line, so thats nice

def summarize(list_1):
    return "The sum of {} is {}".format(list_1, add_list(list_1))

You are returning a 'list', you should return a a 'string'. Also, this is a really cumbersome way to do it, it would be better to use the '.format()' method:

the_number = 6
"Your string, and the number {}.".format(the_number)

or you could use string concatenation:

the_number = 6
"Your string, and the number " + str(the_number) + "."

Thank you Stone and Mikael. You were right. I used Stone's summarize function to get past it. I have saved the code in my PythonAnwhere account. Going to remember this one. Cost me a couple late nights before finally breaking down and asking the forum.

Thank you both for your help.

Cheers, - Ben

Its all part of the struggle ... No worries. Hoes that saying go? It's not the destination but the journey ... Anyway, I'm committed to learning and using Python and your course is helping me achieve this objective.

Cheers,

• Ben