Use a queue when order matters

15-minute session: read for 3 minutes, trace for 3, experiment for 7, and complete the check for 2. Spend longer whenever you need.

FIFO removes the oldest item first. Use a deque for a work queue instead of repeatedly removing index zero from a long list. Specify capacity and what happens when it fills. Test empty, one-item, and full states; an efficient structure still needs a correct policy.

Practice and evidence: Predict the example or draw its state transitions. Change one assumption, test the boundary, and record the actual result. Explain what this small model does not establish about a production system.

from collections import deque
queue=deque(["A","B"])
print(queue.popleft())
queue.append("C")
print(list(queue))

Expected result: A ['B', 'C']

Practice and evidence

Keep three notes: your prediction, the actual result, and why they match or differ. The completion check grades understanding; the practice task builds skill.