PYTHON

python __init_subclass__

In [16]: class Foo:
    ...:     def __init_subclass__(cls):
    ...:         print('ok')
    ...:         print(cls.att)

In [17]: class SubFoo(Foo):
    ...:     att = 1
    ...:     pass
    ...:
ok
1

# So: __init_subclass__ runs everytime that Foo is subclassed.
# Also: the argument `cls` of __init_subclass__ is the subclass.

python __init_subclass__

class Philosopher:
    def __init_subclass__(cls, default_name, **kwargs):
        super().__init_subclass__(**kwargs)
        print(f"Called __init_subclass({cls}, {default_name})")
        cls.default_name = default_name

class AustralianPhilosopher(Philosopher, default_name="Bruce"):
    pass

class GermanPhilosopher(Philosopher, default_name="Nietzsche"):
    default_name = "Hegel"
    print("Set name to Hegel")

Bruce = AustralianPhilosopher()
Mistery = GermanPhilosopher()
print(Bruce.default_name)
print(Mistery.default_name)