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Kind of a radical idea but IMHO in a high-level language (i.e. not C++ or Rust) the real mistake is structs/classes with mutable fields. None of those problems exist in that world.

It's not very ergonomic, but if you start from that assumption you could have ad-hoc syntactic support that desugars to a limited version of an optics library.

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It baffles me that the PEP to add frozendict is still in draft state. It's obnoxious to try and create truly immutable datatypes in Python for... I have no idea why.

frozendict (PEP 416) isn’t in draft, it is rejected

frozenmap (PEP 603) is in draft.

Ah right, I'm not sure how they're significantly different. Regardless, not having a immutable dictionary-type is just... frustrating.

I’ve used types.MappingProxyType on occasion for this

That's ultimately what I ended up using, but it seems not ideal considering the underlying data is still mutable and you still have to maintain a reference to it somewhere to prevent GC

We always use dataclasses with frozen=True to make them immutable.

Same. I treat them as immutable DTOs [0], or "value objects" if you will instead of "just a plain class". An unfortunate drawback is that not everyone is familiar with the concept of immutability, especially in the world of Python. It can also be confusing to explain how "frozen dataclasses are not actually the Python classes you know" :-/

[0] https://en.wikipedia.org/wiki/Data_transfer_object

This should be the default, with the fewest keystrokes and the least visual clutter. Mutable state should be the special case that you need extra syntax for.

So, like Erlang?

What’s an example of a language that does this by default?

Common Lisp Object System might do something like that?

Idiomatic usages of ML-family languages (Haskell, OCaml) are very close to that.

Rust

I'd rather gouge my eyes out than work with Rust code. Horrific.

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