Ah! I've never looked at the book or the MIT course materials.  I see that an update to the book is planned for next year and that 3.5 would have been current when the current edition of the book was published. Generally, changes between recent Python feature releases are upward compatible. Off the top of my head, I can't think of any changes at the Python source level that would cause examples written for 3.5.x to fail on 3.8.x. Perhaps you could ask around online but, rather than trying to debug what's going wrong with your 3.5.x installation, I think you would be better off with 3.8.6. You can just install it on top of 3.5.x. Good luck!