[Python-Dev] Dataclasses, frozen and __post_init__

[Eric V. Smith]

On 2/17/2018 2:35 PM, Guido van Rossum wrote:
> PS. I have to ponder why frozen dataclasses don't use `__new__`.

As I'm sure everyone is now aware after the rest of this discussion: 
it's because the returned object isn't really immutable.

That said, I have threatened to create a decorator similar to 
typing.NamedTuple that has the @dataclass features (except maybe 
__post_init__) and returns a class that does inherit from tuple, in 
which case it really would use `__new__`. I'll save that for 3.8, if it 
ever happens. There's a lot there to think about, first. For now, 
typing.NamedTuple is the way to go if you want something based on 
namedtuple yet using type hints.

Eric