Remove __slots__ from builtins.object

[sobolevn]

I invite everyone to discuss this problem 🙂

Technically, object does not have __slots__ defined:

>>> object.__slots__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'object' has no attribute '__slots__'. Did you mean: '__class__'?
>>> object().__slots__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'object' object has no attribute '__slots__'. Did you mean: '__class__'?

And its subclasses do not have __slots__:

>>> class Bar(object):
...     ...
... 
>>> Bar.__slots__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'Bar' has no attribute '__slots__'. Did you mean: '__class__'?
>>> Bar().__slots__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Bar' object has no attribute '__slots__'. Did you mean: '__class__'?

We need to explicitly specify that some type has __slots__.

Maybe it is better to special-case __slots__ in type-checker? It is not hard to check that class-level field named __slots__ is str | Iterable[str] 🤔

Related python/mypy#11891 and python/mypy#11885

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[srittau]

Considering that all checks pass and primer has no complaints, I'm +1 on this change.

[Akuli]

I don't have a strong opinion on this, as I don't think there's much practical impact. Even __slots__ = ("foo", "bar") is quite rare.

[sobolevn]

I don't have a strong opinion on this, as I don't think there's much practical impact.

See python/mypy#11885