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Thanks for your feedback Petr!
The PEP will not affect CPython directly except for the addition of the dataclass_transform decorator in typing.py.
Could this be also said in the PEP itself?
Yes, good point.
Do you not plan to apply the decorator to dataclass itself? Will dataclasses.dataclass not get a __dataclass_transform__ attribute at runtime?
No, we were not planning to decorate dataclass with dataclass_transform.
it would be better to link to the current documentation than to the 4-year-old document that first proposed adding dataclasses... Same for later references to that PEP.
That's fair, although I think the existing references to PEP 557 are ok because we're linking to specific, relevant parts of that document. Would adding a link to the docs in the abstract be satisfactory? I just created a PR for this and your first point above. [1]
Are the semantics expected to evolve if new features are added to dataclasses? Or to other popular libraries that work like dataclasses?
dataclass_transform is expected to evolve with dataclass. I recently added a paragraph to Rationale that explains this. We would consider evolving dataclass_transform based on new features in other dataclass-like libraries. But we would prefer that these libraries become more similar to stdlib dataclass either by changing their APIs or proposing new dataclass features. Thanks, Erik [1]: https://github.com/python/peps/pull/2390