C3W1 argument must be an iterator

I finished the coding and it works as expected (output is the same as the expected output across different sections). However, I got an error message after submitting the code, which says “There was a problem compiling the code from your notebook. Details:
argument 1 must be an iterator”. I am not sure the argument 1 of which function. Anyone can help? Thanks.

Please update your post with the expanded screenshot of the grader feedback. This helps the reader(s) understand which graded portion has this problem.

Hi Balaji,

Thanks for your response and please see the attached to find my code. I was stuck here but cannot figure out why.

XF

[code removed - moderator]

Don’t post code on a public topic. You are welcome to share the stacktrace.
It seems like you want me to look at your notebook. Click my name and message your notebook as an attachment.