Expert Python Programming - Third Edition

Non-deterministic caching

Caching non-deterministic functions is trickier that memoization. Due to the fact that every execution of such a function may give different results, it is usually impossible to use previous values for an arbitrarily long amount of time. What you need to do instead is to decide for how long a cached value can be considered valid. After a defined period of time passes, the stored results are considered stale and the cache will need refreshing with a new value.

Non-deterministic functions that are usually a subject of caching often depend on some external state that is hard to track inside your application code. Typical examples of components include the following:

• Relational databases, or generally any type of structured ...