Test your knowledge: function caching

Check when caching is safe, how cache and lru_cache differ, and how to inspect, invalidate, and constrain stored results.

5 questions ~5 min Intermediate

Knowledge check

Check when caching is safe, how cache and lru_cache differ, and how to inspect, invalidate, and constrain stored results.

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When is caching a function result generally appropriate?

Caching can skip the function body on a hit. It is best when the result is stable for the arguments and reusing the returned object is safe.
What does @cache mean for the number of entries retained?

@cache is the unbounded form. Choose lru_cache(maxsize=...) when the cache needs a capacity limit.
Why does a cached function reject a list argument by default?

The cache keys arguments in a dictionary-backed structure, so the arguments must be hashable.
A cached lookup depends on a mutable mapping that has changed. What should happen before reading the updated result?

The cache does not observe changes to unrelated external state. cache_clear() removes old entries so the next call computes again.
What does lru_cache(maxsize=2) guarantee about stored entries?

A bounded LRU cache retains no more than its configured maximum and can evict least-recently-used entries.

When is caching a function result generally appropriate?