[jsonbailey]

Summary

Remove the expiringdict dependency. The SDK now uses a small private class, ldclient.impl.expiring_cache.ExpiringCache. The persistent-store cache and the Big Segment membership caches (sync and async) use it.

expiringdict has had no release since 2022, and the SDK uses only a few of its features. The new class keeps this behavior:

• Each entry expires a fixed time after it is written. Reads do not extend its life.
• When the cache is full, the first-written entry is evicted (FIFO, not LRU).
• Replacing an existing key does not evict a different entry.
• All operations are thread safe. The callers do not lock around the cache.

Two small differences:

• Expiry uses time.monotonic(), not time.time(), so wall-clock changes no longer affect it.
• Rewriting an existing key always moves it to the newest eviction position. In expiringdict 1.2.2, a rewrite keeps the key's original position unless the cache is full.

Both projects are Apache 2.0. The class is new code, not a copy.

This ships in the current major version. An application that imports expiringdict without declaring it as its own dependency must now add it.

---

Note

Overview
Removes the expiringdict dependency and wires caching through a new in-tree ExpiringCache (ldclient.impl.expiring_cache).

Persistent feature-store caching (CachingStoreWrapper) and Big Segment membership caches (sync and async managers) now instantiate ExpiringCache with the same capacity and TTL settings as before. The new type is thread-safe and exposes the dict-like surface those call sites already use (get, __setitem__, pop, clear, __len__).

Semantics are intentionally aligned with the old library: TTL is measured from last write, reads do not refresh expiry, and overflow evicts the first-written entry (FIFO, not LRU). One deliberate difference: expiry uses time.monotonic() instead of wall clock time, so NTP or manual clock changes no longer shorten or extend cache lifetimes.

Packaging: expiringdict is dropped from main and docs optional dependencies. A large dedicated test suite covers TTL, eviction, and concurrency; an existing cache-lifecycle test comment is updated to refer to “the old cache” generically.

^{Reviewed by Cursor Bugbot for commit b60b3fd. Bugbot is set up for automated code reviews on this repo. Configure here.}

[keelerm84]

On the open question: I'd ship this in a minor release. An application that imports expiringdict without declaring it depends on our internals, and a changelog note covers that case.