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slots declared on attrs-decorated class are ignored/lost

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@anshurajbisoyi98-ctrl ci sta già lavorando.

Dal 3/10/2026.

  • #1638 di @anshurajbisoyi98-ctrl — aperta

Valutazione

Difficoltà
3/5
Tempo stimato
1-2 giorni
Idoneità per principianti
68/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
python
Ambito
developer-experience

Direzione di ricerca

Start by reproducing the two examples in the issue and compare how attrs processes slots declared on the class with slots inherited from a base class. Trace the slot-processing entry point and add a regression test for preserving a class-declared private slot; done means assigning that slot works while it remains outside attrs fields and generated methods.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

If a slotted attrs class declares its own slots, those slots are lost/ignored when the class is processed by attrs. E.g.

@attrs.define
class A:
    __slots__ = ("private",)

    public: str = "foo"

a = A()

a.private = 1

produces the error TypeError: descriptor 'private' for 'A' objects doesn't apply to a 'A' object.

However, declaring an attrs class that subclasses a class that defines slots, the parent class's slots are preserved. E.g.

class Base:
    __slots__ = ("private",)

@attrs.define
class B(Base):
    public: str = "bar"

b = B()

b.private = 1

sets the slots attribute without issue.

Is this intentional behavior or dictated by the design of attrs? I've looked at the code and it looks like it goes out and gets slots defined on base classes and adds them to the slots defined on the new class. Using that same method, it doesn't look like it would be hard to preserve slots declared on the slotted attrs class itself, but I haven't tried to code it and I don't know if it would break something I'm not seeing. (Note that declaring __slots__ on a class decorated with @attrs.define(slotted=False) doesn't work for other reasons, so this question/issue really only applies to slotted attrs classes).

It can often be useful to have private attributes on a class that may be used for internal instance management but aren't really part of the data model represented by the class and should be ignored by attrs--not included in the init or hash or equality functions. This can, of course, be accomplished by declaring the attribute with init=False, hash=False, and eq=False, but the attribute still shows up in the collections returned by attrs.fields or attrs.fields_dict and is serialized by attrs.asdict (which, similarly, can be worked around with a filter). Declaring slots would be a simple way to allow an instance to have attributes that attrs is entirely unaware of. Using a base class is a workaround, but it would be preferable not to have to create a separate base class or mixin solely to add extra slots.

Lingua principale
Python
Stelle
5.9k
Fork
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Merge medio
3g 12h
PR unite (30g)
3

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