metaclass_example.py

class ParentMeta(type):
    def __new__(cls, name, bases, cls_dict):
        cls = super().__new__(cls, name, bases, cls_dict)
        cls.items = cls.items.copy()
        return cls
        
class Parent(metaclass=ParentMeta):
    items = []
        
class Child(Parent):
    pass


Parent.items.append(1)
Child.items.append(2)
assert Parent.items == [1]
assert Child.items == [2]
assert Child.items is not Parent.items