[macintux]

Speaking as someone who Friday had to fix an embarrassing bug in my Python code because lists aren’t immutable when passed to another function, I like the way you think.

I will say, however, that what I want from Python isn’t actually “frozen” data structures but cloned ones (or, like some/most FP languages, structures with nested values that are only cloned when necessary).

Vals, not vars.

[BerislavLopac]

> lists aren’t immutable when passed to another function

Well, lists are never immutable in Python; you want to use tuples for that.

[macintux]

True, what I really want is referential transparency, not immutability per se.

I’ve only used tuples in Python as a small data structure, will have to experiment with using them as a list substitute, thanks.

[BerislavLopac]

Just keep in mind that a tuple's elements can still be mutable, so it's not a "frozen" data structure throughout.

[diegojromero]

Interesting idea, instead of a deep clone, would it be something similar to the copy-on-modify pattern?

[macintux]

Copy on modify would work, certainly. The term I was forgetting when I wrote that is “persistent” data structures, but I’m not sure whether it’s practical to implement persistent structures in a non-functional language like Python.

https://hypirion.com/musings/understanding-persistent-vector...