super's behavior and method resolution order in multiple inheritance

super_mro.py

"""
MRO (Method Resolution Order) with multiple inheritance is resolved via
a linearization algorithm that flattens a tree. In some cases, super()
is not bound to a classes superclass, but instead to a sibling depending
on the object's MRO.
"""


class Base:
    def __init__(self, field, **kwargs):
        self.field = field
        mro = " -> ".join([c.__name__ for c in self.__class__.__mro__])

        print(f"Base.__init__({kwargs})")
        print(f"mro: {mro}")

    def instance_method(self):
        print(f"Base.instance_method called from: {self.__class__.__name__}")

    def __contains__(self, string):
        return string in self.field

    def __len__(self):
        return len(self.field)


class Class1(Base):
    def __init__(self, field, **kwargs):
        print(f"Class1.__init__({kwargs})")
        self.field1 = kwargs.pop("field1", "default1")
        super().__init__(field, **kwargs)

    def instance_method(self):
        print("Class1")
        super().instance_method()


class Class2(Base):
    def __init__(self, field, **kwargs):
        print(f"Class2.__init__({kwargs})")
        self.field2 = kwargs.pop("field2", "default2")
        super().__init__(field, **kwargs)

    def instance_method(self):
        print("Class2")
        super().instance_method()


class Class3(Class1, Class2):
    def __init__(self, field, **kwargs):
        print(f"Class3.__init__({kwargs})")
        super().__init__(field, **kwargs)

    def instance_method(self, derived_class=None):
        print()
        print("=" * 60)
        print(f"super of {derived_class.__name__}")

        if derived_class:
            super(derived_class, self).instance_method()
        else:
            super().instance_method()
        print("=" * 60)


if __name__ == "__main__":
    class3 = Class3("data", field1="data1")

    class3.instance_method(derived_class=Class3)
    class3.instance_method(derived_class=Class2)
    class3.instance_method(derived_class=Class1)