What is all the info in the info window in Idle?

[DeaD_EyE]

Not all classes do have a dict. If the classvariable __slots__ is used, then only the names from the supplied sequence are available and there is no __dict__. This is used to save memory. If you have only one instance of the class, you don't care. If you have one million, you care.

class Foo:
    __slots__ = ("x", "y")


Foo().__dict__

Output:
AttributeError: 'Foo' object has no attribute '__dict__

Dataclasses supports this too:

from dataclasses import dataclass

@dataclass(slots=True)
class Foo2:
    x: int
    y: int

If you use a class with slots, you cannot add new attributes to the class.