Test your knowledge: Python Priority Queues

Review

1. What does heap[0] represent in a valid min-heap?

   The min-heap invariant guarantees that its smallest item is stored at index 0.
2. What does heapq.heapify(values) do?

   heapify() changes the list in place to satisfy the heap invariant; it does not promise a fully sorted list.
3. What problem does a unique sequence number solve in (priority, sequence, task) entries?

   The sequence number makes ties deterministic and is compared before the task payload.
4. How does heapreplace(heap, item) differ from heappushpop(heap, item)?

   heapreplace always returns the old minimum then inserts item; heappushpop returns the smaller of item and the previous minimum.
5. When should a program use queue.PriorityQueue instead of a plain heapq list?

   queue.PriorityQueue provides locking and queue coordination semantics for threaded producer/consumer usage.