One issue with this is that arbitrary Python code can have arbitrary side-effects. Your suggestion reminds me a lot of fine-grained reactivity like in SolidJS,

One issue with this is that arbitrary Python code can have arbitrary side-effects. Your suggestion reminds me a lot of fine-grained reactivity like in SolidJS, which makes sense, since spreadsheets basically operate on reactive programming. Some great articles by Ryan Carnatio on the topic. The side-effects thing comes in if a user puts in some side-effect in a dependent cell, which is equivalent to adding side-effects in a memo in reactive-speak.