deque vs list in Python: Which Is Faster for a Queue?

Intro — what this post promises

For a FIFO queue in Python, collections.deque beats a list: with append + popleft vs append + pop(0) on Python 3.13.5, deque was about 1.2x faster on a near-empty queue, 2.6x at 1,000 queued items and about 31x at 10,000 (18.6M vs 605k cycles/s). The problem is removing from the front of a list, not lists in general, because list.pop() from the end drained 50k items as fast as deque did.

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Lab honesty (1 Oct 2026 IST): Python 3.13.5. Affiliates: 0. FIFO cycle = one append + one front pop, keeping length ≈ S.

Verdict up front: at S=0–100 deque is only ~1.2–1.2× list. At S=1 000 already ~2.6×. At S=10 000 ~31× (18.6M vs 605k cycles/s). Draining 50k with pop(0) is ~255k/s vs deque ~31.6M.

Arms

Lab topology

FIFO S in {0, 100, 1000, 10000, 50000}
M scaled down for large S (still p50 ops/s)
Drain N in {1000, 10000, 50000}
Metric: p50 wall → cycles/s or pops/s

Script: lab-evidence/54-deque-vs-list-queue/results/run_lab.py.

Lead table — FIFO cycles/s (p50)

At S=10k, list pays ~1654 ns/cycle vs deque ~54 ns.

Drain and append baselines

list.pop() from the end matches deque drain speed — the bug is front removal, not “lists are slow.”

Pitfalls

1. Benchmarking empty-queue FIFO only — S≈0 hides the O(n) shift.
2. Using list as a queue “until it hurts” — at S=1k it already hurts on this box.
3. Confusing stack (pop()) with queue (pop(0)) — different asymptotics.
4. Indexing into a deque — O(n) for middle access; use a list if you need random access.

When to pick what

Reproduce

python3 lab-evidence/54-deque-vs-list-queue/results/run_lab.py

Evidence: /workspace/lab-evidence/54-deque-vs-list-queue/results/.

Closing

list.pop(0) does not stay fine. On this box deque FIFO is ~2.6× at S=1k and ~31× at S=10k. Drain 50k: deque ~32M/s vs list pop(0) ~255k. Use deque for queues; keep list for stacks and random access.

FAQ

Is deque faster than list in Python?

For queue work, yes. Draining 50,000 items, deque.popleft ran at about 31.6M pops/s vs about 255k/s for list.pop(0). For appends only, the two are close (41.8M vs 36.9M/s).

Why is list.pop(0) slow?

Removing the first item shifts every remaining item, so the cost grows with queue length. At 10,000 items a list cycle cost about 1,654 ns vs about 54 ns for deque.

When should I still use a list?

For stacks (append/pop from the end) and random access. Indexing into the middle of a deque is O(n), so use a list when you need positional reads.