This cell is returning an error and is uneditable. Can someone please explain why does this happen?
The source of the problem is explained here.
We have locked all ungraded cells because ungraded cells are not supposed to be edited. Editing it can cause trouble to the autograder and ends up failing the submitted assignment.
Even if an error occurs in a cell, the source of the problem does not necessarily come from that cell, because in that cell we can be calling functions that were defined in previous cells. Therefore, if you have defined a function with some mistakes but you did not call it right the way, then no error will be shown. However, if you call that function a few cells later, then it will show an error that can be traced back to the function defined in some earlier cell. In my explanation in the other post, it is exactly such kind of case.
Lastly, you can unlock any cells and the instruction to do so is included in the last part of the assignment notebook, but we strongly suggest you only to do so after you have successfully submitted the assignment. Making change to ungraded code cell will not help you pass the assignment, but it can make things worse.
I understand Raymond. Thank you for your suggestions
You are welcome, @Prakhar_Arya!