>"You can use it to cache values between function calls:" and I really hope nobody does that.
That default parameter is a mutable global variable and languages like Rust have effectively banned mutable statics for good reasons that I personally am discovering myself by messing around with UnsafeCell inside statics and even I personally am starting to think that mutable statics are at best a necessary evil, but not one you want to rely on as your go to solution.
I'm not concerned about the global. The problem is it's global but doesn't look like it, or looks like a mistake. You want a global cache in Python, there are easy and much better ways.
That default parameter is a mutable global variable and languages like Rust have effectively banned mutable statics for good reasons that I personally am discovering myself by messing around with UnsafeCell inside statics and even I personally am starting to think that mutable statics are at best a necessary evil, but not one you want to rely on as your go to solution.