avoid unmarshallable object errors

app.py

@@ -174,8 +174,28 @@ def evaluate_submission(file_obj, debug=False):
         print(f"EVALUATING: {file_path}")
         print(f"{'='*60}\n")
         
-        spec = importlib.util.spec_from_file_location("student_module", file_path)
+        # Clear any cached bytecode to avoid unmarshallable object errors
+        import sys
+        import pathlib
+        if file_path in sys.modules:
+            del sys.modules[file_path]
+        
+        # Remove .pyc files if they exist
+        py_file = pathlib.Path(file_path)
+        pycache_dir = py_file.parent / '__pycache__'
+        if pycache_dir.exists():
+            for pyc_file in pycache_dir.glob(f'{py_file.stem}*.pyc'):
+                try:
+                    pyc_file.unlink()
+                except:
+                    pass
+        
+        # Import with a unique module name each time
+        import time
+        module_name = f"student_module_{int(time.time() * 1000000)}"
+        spec = importlib.util.spec_from_file_location(module_name, file_path)
         student_module = importlib.util.module_from_spec(spec)
+        sys.modules[module_name] = student_module
         spec.loader.exec_module(student_module)
         
         report = [f"## Results:\n"]