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persistent deque

Language: Python · Sphere: programming · Category: Data Structures

What it does

Doubly-linked deque that serializes its full contents to a pickle file after every mutation and reloads that state on construction.

Use when a deque must survive process death: append/appendleft/pop/popleft mirror collections.deque, an optional maxlen evicts from the opposite end, and each operation persists to disk.

Guarantees (self-test): a fresh instance recovers exact ordered state after the owning instance is dropped, a 200-op fuzz with periodic reloads tracks collections.deque, maxlen evicts the correct end, and empty pops raise IndexError.

Guarantee

When it runs, persistent deque guarantees dq.pop() == 2 and dq.popleft() == 0 and (list(dq) == [1]); list(dq) == [0, 1, 2]; list(recovered) == [-1, 1, 7] (proven by run).

Checkable constraints:

  • list(dq) == [0, 1, 2]
  • dq.pop() == 2 and dq.popleft() == 0 and (list(dq) == [1])
  • list(recovered) == [-1, 1, 7]
  • len(recovered) == 3
  • d.pop() == oracle.pop()
  • d.popleft() == oracle.popleft()
  • list(d) == list(oracle)
  • list(d) == list(oracle) and len(d) == len(oracle)

Verification evidence

  • Green-run: ✓ passes (re-run under the extractor's gate)
  • Constraint strength: recovery (truth-pinned)
  • Independent oracle: — none yet (green-run candidate; not an axiom under the frozen ruler)
  • Peer review: unreviewed

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