First, I finished this exercise with only minor complication. As much as I checked the forum, this was quite common. I put the list students = [lloyd, alice, tyler] in the function get_class_average (like so
results = 
students = [lloyd, alice, tyler]
for student in students:
I tried a few things, like deleting that list, and it worked. But then I wondered, how come the function get_class_average know who these students are if we didn't define the list students anywhere?
Much thanks to all who take time for this question