Week 1 Assignment ( 0 grade)

I have complite all the excises,but when I submit, I get the 0 grades, and when I run the cells,I didn’t find the “Error” hints. Someone could give me some help?

What does the grader feedback say?

After I update , I submit again ,and have the same problem, here is the feedback ‘Cell #6. Can’t compile the student’s code. Error: TypeError("‘NoneType’ object is not iterable")’

The “NoneType” error implies that perhaps, somewhere in the notebook, you’ve left a “None” statement that needs to be replaced.