How to define class field in Python that is an instance of a class?

I want to get a specific class instance in the class's namespace. In C# this would look like this:

public struct Foo
{
    public readonly static Bar = new Foo();
}

The only idea I have is to assign an instance right after the class definition (monkeypatch):

class Foo:
    def __init__(self, spam):
        self.spam = spam
Foo.bar = Foo(42)

But I want to provide instance in class definition, like this:

class Foo:
    ...
    bar = Foo(42)

And interface like this:

from foo import Foo
bar = Foo.bar

The last line in definition gives a syntax error because Foo is not yet defined. Is there a way to overcome this constraint except monkeypatching class?

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