Stepping back, I think part of your surprise toward `lru_cache` stems from familiarity with out-of-core or distributed caches, where the immutability of cached

Stepping back, I think part of your surprise toward `lru_cache` stems from familiarity with out-of-core or distributed caches, where the immutability of cached values is simply imposed by the architecture. In a distributed cache, modifying the cached value in-place means making another API call, so you can’t mutate the cached object accidentally because you mistook it for a copy. The only way you can have this confusion is if the actual cached object could be somehow returned. That only happens when everything in the cache is actually just a Python object in your same process.