Let's try to tie everything we've learned together with a larger example. We'll be developing an automated grading system for programming assignments, similar to that employed at Dataquest or Coursera. The system will need to provide a simple class-based interface for course writers to create their assignments and should give a useful error message if it does not fulfill that interface. The writers need to be able to supply their lesson content and to write custom answer checking code to make sure their students got the answer right. It will also be nice for them to have access to the students' names to make the content seem a little friendlier.
The grader itself will need to keep track of which assignment the student is currently working on. A student might make several attempts at an assignment before they get it right. We want to keep track of...