gh-143969: Fix frozen+slotted dataclass __setattr__ crash ambiguity #143971
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sobolevn
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Please, add a test case. And please, do not change lines that are just changed because of the formatting. Only change lines that are directly related to your change :)
Thanks for the PR!
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Lib/dataclasses.py
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| ' raise FrozenInstanceError(f"cannot assign to field {name!r}")', | ||
| f' super(cls, self).__setattr__(name, value)'), | ||
| ' raise FrozenInstanceError(f"cannot assign to field {name!r}")', | ||
| ' object.__setattr__(self, name, value)'), |
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I don't think that this fix is correct, because it ignores parent's __setattr__ method.
The root cause of the bug might be something related to the __closure__ cell of the property? See https://github.com/python-attrs/attrs/blob/28526a872ec882c69d5d30932c1a520ef2520309/src/attr/_make.py#L959-L990 for the context.
Or it might be not :)
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I am really sorry, I pushed the object.setattr change just before seeing your comment!
You are right, bypassing super breaks inheritance for any parent classes that override setattr. I will revert the object change locally and look into the closure / class cell solution you linked. I'll update the PR once I have a fix that respects the MRO. Thank you for the heads up! I'm learning a lot from this!
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…osure cells When a dataclass is frozen and uses slots, the class object is replaced. This causes generated methods using super() to fail because their closure cells point to the old class. This fix updates the closure cells in the generated methods to point to the new class.
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| Fixed a crash in frozen slotted dataclasses where assigning to an attribute | |||
| could raise an internal TypeError instead of failing cleanly. | |||
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| could raise an internal TypeError instead of failing cleanly. | |
| could raise an internal :exc:`TypeError` instead of failing cleanly. |
Fixed Misleading "Not an instance or subtype" error when assigning to property of frozen, slotted dataclass.
Fix a crash in frozen dataclasses with slots where the generated
setattr and delattr methods used super(cls, self).
When slots rebuild the class, the captured cls no longer matches the
instance type, causing a TypeError at runtime.
Use object.setattr and object.delattr instead to preserve frozen
semantics safely.
gh-143969