Grader error - "Details: name 'os' is not defined"

The grader output when submitting the jupyter notebook for course 2 week 1 has an error and displays the following:

There was a problem compiling the code from your notebook. Details:
name 'os' is not defined

I downloaded this notebook from my google colab where I ran it so I’m confused why the grader experiences this issue. All I did manually was add the “graded” tags that were missing for the cells that had the comment “GRADED”.

There should be no need for you to manually edit cell metadata. If refreshing the workspace doesn’t fix grader issues, please click my name and message your notebook as an attachment.

Please look at metadata of the 1st cell in your notebook. It doesn’t contain the graded entry in tags like this:

I just downloaded the starter code from google colab and it has the correct metadata. Do start again and edit cells only at places where required.

Great, thank you. Re-downloading the starter notebook from Colab and copying the code worked for me.