I concur with Victor.  The proposed API change defeats the purpose of the cache.  By design, the intent of the cache is to reuse the previously computed value.

I can add something like this to the docs: """In general, the LRU cache should only be used when you want to reuse previously computed values.  Accordingly, it doesn't make sense to cache functions with side-effects, functions that need to create distinct mutable objects on each call, or impure functions such as time() or random()."""