[Python-Dev] Dataclasses, frozen and __post_init__

[Guido van Rossum]

On Tue, Feb 20, 2018 at 1:37 PM, Eric V. Smith <eric at trueblade.com> wrote:

> 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.
>

But then the class would also inherit a bunch of misfeatures from tuple
(like being indexable and having a length). It would be nicer if it used
__slots__ instead. (Also, the problem with __slots__ is the same as the
problem with inheriting from tuple, and it should just be solved right,
somehow.)

-- 
--Guido van Rossum (python.org/~guido)
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-dev/attachments/20180220/f15d80ea/attachment.html>