Implement Python LRU cache with args and persistence
Overview
This question evaluates a candidate's ability to design and implement an LRU cache in Python that supports variable-length positional and keyword arguments with canonical, deterministic hashing for semantically equivalent calls and O(1) get/put via a hash map plus a doubly linked list; it falls under the Coding & Algorithms domain and primarily tests practical implementation skills, API robustness, hashing/equality subtleties, and algorithmic complexity guarantees. The persistence follow-up evaluates understanding of serialization and storage design — on-disk formats, versioning, and atomic write strategies — and compares trade-offs between binary pickle and JSON-based serialization in terms of security, compatibility, and performance, reflecting both conceptual design and practical system-level considerations.
Implement an LRU cache in Python as a decorator or class that correctly supports variable-length positional arguments and keyword arguments. Ensure that calls are keyed canonically so keyword ordering does not matter, unhashable arguments are converted to deterministic, hashable representations, and semantically equivalent calls map to the same cache entry. Provide O(
- get/put using a hash map plus a doubly linked list. Follow-up: add persistence so the cache can be snapshotted to disk and restored on process start. Specify an on-disk format, versioning, and atomic write strategy; compare trade-offs between pickle and a JSON-based manual serialization (security, compatibility, performance); and implement a simple, safe approach.