You can cache function results yourself in Python if you want to - my implementation also sums up the tokens used by the calls to the functions.
Influencing optimization isn't possible using regular Python-based custom SQL functions though. I think you can influence that stuff in SQLite if you create more complex virtual table functions, but those aren't exposed through the regular Python sqlite3 module yet.
Thanks for the clarifications. Token summation is a cool optimization :)
Query optimizers in SQL database systems typically optimize based on the time to execute the function on a local server. The token summation optimization generalizes time-based optimization of local functions to dollar-based optimization for remote functions.
Influencing optimization isn't possible using regular Python-based custom SQL functions though. I think you can influence that stuff in SQLite if you create more complex virtual table functions, but those aren't exposed through the regular Python sqlite3 module yet.