Question 117 of 498
PCEP Control Flow, Loops, Lists and Logic Practice Question
A developer is debugging a function that uses a while loop to reverse a list in place. The current code causes an infinite loop. Which three modifications would likely fix the infinite loop? (Select three.)
⚠ Common exam trap
Python Institute often tests the misconception that adding a break or using a temporary variable alone can fix an infinite loop, when the root cause is missing index updates that prevent the loop condition from becoming false.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Ensure the end index is decremented each iteration
In a while loop that reverses a list in place, the end index must be decremented each iteration to move the end pointer toward the center. Without decrementing the end index, the loop condition (e.g., start < end) may never become false, causing an infinite loop. This ensures the two pointers converge and the loop terminates.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Ensure the end index is decremented each iteration
Why this is correct
Necessary to eventually meet start condition.
- ✗
Add a break statement after the swap
Why it's wrong here
Would exit after first swap, not reverse the entire list.
- ✗
Use a temporary variable for the swap
Why it's wrong here
Good practice but does not fix the infinite loop.
- ✓
Ensure the start index is incremented each iteration
Why this is correct
Necessary to eventually meet end condition.
- ✓
Use a for loop instead
Why this is correct
A for loop with a fixed range would not loop infinitely.
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Last reviewed: Jun 30, 2026
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