What is the difference between them in Python 3.7?

[DeaD_EyE]

In this case, theoretically, "arg" should be the class name itself; however, it works as an ordinally argument. Strange. Why? At least, the "rule of first argument of a class" seems to be broken here.
Is this Python's specification?

If I remind right, it was very easy to implement classes in one day into the Python language.
Later it turned out that this kind of implementation opens up further possibilities.

Other languages don't have this feature. So they can't do, what Python is able to do.