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lru cache

Language: Python · Oracle sphere: rust (this file is the Python twin) · Category: performance

What it does

Thread-safe LRU cache with optional per-entry TTL expiry.

A fixed-capacity cache backed by an OrderedDict under an RLock: reads and writes mark keys as recently used, the least-recently-used key is evicted at capacity, and entries may carry a time-to-live after which get() returns None. Use it as a bounded in-process cache where both recency eviction and freshness matter. Guarantees (self-test oracle): LRU eviction order holds, get() refreshes recency (a just-read key survives the next eviction), TTL expiry fires on a fake clock, and concurrent writes from many threads are not lost or corrupted.

Guarantee

When it runs, lru cache guarantees cache.size == 3; cache.get('k1') is None; cache.get('k2') == 'v2' — read from this file's own self-test. The oracle behind this pattern was established on the rust original and is not claimed to have been run against this file.

Checkable constraints:

  • cache.size == 3
  • cache.get('k1') is None
  • cache.get('k2') == 'v2'
  • cache.get('k3') is None
  • cache.get('short') == 's'
  • cache.get('short') is None
  • cache.get('forever') == 'f'
  • cache.delete('forever') is True

Verification evidence

  • Green-run: ✓ passes (re-run under the extractor's gate)
  • Constraint strength: recovery (truth-pinned)
  • Independent oracle: — established on the RUST original and shared by this Python twin (twin agreement is the evidence: consensus, xlang); the original oracle was not executed against this file
  • Peer review: unreviewed

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