Deterministic functions are the easiest and safest use case for caching. Deterministic functions always return the same value if given exactly the same input, so you can generally store their results indefinitely. The only limitation to this approach is storage capacity. The simplest way to cache results is to put them into process memory, as this is usually the fastest place to retrieve data from. Such a technique is often called memoization.
Memoization is very useful when optimizing recursive functions that may need to evaluate the same input multiple times. (We already discussed recursive implementations for the Fibonacci sequence in Chapter 9, Python Extensions in Other Languages.) Earlier on in this book, we tried ...
