I didn't realize it was possible to add slots in that way (slots=True). I
think for normal classes manually defining __slots__ is the common way of
adding __slots__ (at least for me), so it feels weird to me that manually
defining __slots__ instead of adding slots=True produces different
behaviour. That being said, no strong motivation to change it, this fixes
my issue, feel free to close this.

Thanks,
Justin

On Mon, Oct 18, 2021 at 9:25 PM Josh Rosenberg <report@bugs.python.org>
wrote:

>
> Josh Rosenberg <shadowranger+python@gmail.com> added the comment:
>
> When I define this with the new-in-3.10 slots=True argument to dataclass
> rather than manually defining __slots__ it works just fine. Looks like the
> pickle format changes rather dramatically to accommodate it.
>
> >>> @dataclass(frozen=True, slots=True)
> ... class FrozenData:
> ...     my_string: str
> ...
> >>> deepcopy(FrozenData('initial'))
> FrozenData(my_string='initial')
>
> Is there a strong motivation to support manually defined __slots__ on top
> of slots=True that warrants fixing it for 3.10 onward?
>
> ----------
> nosy: +josh.r
>
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> <https://bugs.python.org/issue45520>
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