Fix Bugs in Grade System

I have a compact student-grade management script that runs end-to-end without crashing, yet two key functions are silently wrong. After a recent refactor, both • get_student_grades() • calculate_average() now return the wrong data type, surface unexpected values, or give no output at all. The rest of the program executes, which makes the bugs harder to spot. Your assignment is to trace the logic, uncover the root causes, and fix all eight latent issues I have embedded in this codebase. They cover real-world pitfalls such as mutable default arguments, scope-leaking accumulators, shallow-copy side effects, type mismatches, faulty base cases, boolean slip-ups, attribute typos, and the classic off-by-one error. What I need from you: 1. Clean, working code that produces correct results for every provided test case. 2. A short changelog (a few sentences per bug) explaining what was wrong and how you resolved it. 3. No new libraries—pure Python only—so the script remains beginner-friendly for students who will study the final version. If you can spot and patch these bugs quickly and clearly, this should be a straightforward hour’s work. I’ll verify fixes with my unit tests and accept once both functions behave as expected and the full script passes all checks.

Project ID: 40548452