Refactor exam_take function to use a canonical list of questions for consistent indexing and improved error handling for question navigation

physics/views.py

@@ -188,7 +188,16 @@ def exam_take_overview(request, pk, cid=None, passcode=None):
     )
 
 
-def exam_take(request, pk: int, sk: int, cid: str| None = None, passcode: str| None = None):
+def exam_take(request, pk: int, sk: int, cid: str | None = None, passcode: str | None = None):
+    """Display and handle answers for a single question in a physics exam.
+
+    Behavior and invariants:
+    - Uses a single canonical list of questions (from `exam.get_questions()`) for
+      selection, navigation and sizing so indexes cannot drift.
+    - Validates the incoming question index and raises 404 for invalid values.
+    - Supports candidate (cid) and logged-in user answers.
+    """
+
     exam = get_object_or_404(Exam, pk=pk)
 
     if not exam.active:
@@ -198,25 +207,23 @@ def exam_take(request, pk: int, sk: int, cid: str| None = None, passcode: str| N
 
     cid_user_exam = exam.get_or_create_cid_user_exam(cid=cid, user_user=request.user)
 
-    # Use a single, canonical list of questions for all indexing/navigation
-    # operations to avoid mismatches between different querysets or orderings.
+    # Canonical questions list for consistent indexing/navigation
     questions = list(exam.get_questions())
 
-    # Validate sk and select the current question
+    # Normalize and validate provided index
     try:
-        sk = int(sk)
+        index = int(sk)
     except Exception:
         raise Http404("Invalid question index")
 
-    if sk < 0 or sk >= len(questions):
+    if index < 0 or index >= len(questions):
         raise Http404("Question not found in exam")
 
-    question = questions[sk]
-
+    question = questions[index]
     exam_length = len(questions)
 
-    # Since we're using the canonical list, the positional index is sk.
-    pos = sk
+    # local numeric position equals the validated index
+    pos = index
 
     if cid is not None:
         answer = question.cid_user_answers.filter(cid=cid, exam=exam).first()