Why exactly in this example is it giving me "NoneType object is not subscriptable"?

https://www.codecademy.com/paths/computer-science/tracks/cspath-flow-data-iteration/modules/dspath-lists/lessons/python-functions-lists-cc/exercises/append-sum

Hello,

in the end I looked for the solution to this exercise but am however still curious to know why exactly my code was given “NoneType object is not subscriptable”, that way I hopefully don’t repeat the same error. So this was my code:

def append_sum(lst):
  sum1 = lst[-1] + lst[-2]
  lst = lst.append(sum1)
  sum2 = lst[-1] + lst[-2]
  lst = lst.append(sum2)
  sum3 = lst[-1] + lst[-2]
  lst = lst.append(sum3)
  return list

Thank you.

What does your call to the function look like?

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This is what is written at the end of the exercise:

print(append_sum([1, 1, 2]))

I apologize if I’m not giving you the answer you’re looking for.

That line isn’t still in the code, is it?

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Hi @ai-2090,

The NoneType object, namely None, is what is assigned to lst in this statement:

  lst = lst.append(sum1)

Then your code attempts to subscript lst here:

  sum2 = lst[-1] + lst[-2]

See the following:

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Thank you @mtf and @appylpye for your help, I think I’m getting it now, thanks also to a reply I got on my other topic concerning NoneType. Later in the day I’ll go as well through the link appylpye provided.

Have a nice day.

2 Likes