Python：确保 class 属性不在公共继承树之间共享

Question

我有种好像在哪里见过的感觉，但我不确定那是重建的记忆还是真的存在。无论如何，我找不到对这种情况的参考：

class A:
    a = 1

class B(A):  # should have it's own class attribute 'a'
    pass

class C(A):  # should have it's own class attribute 'a' and newly defined 'c'
    c = 3

在上面的例子中，A.a is B.a is C.a。但是，我实际上希望在保持这种结构的同时将它们分开。这是有充分理由的，我不想讨论实例变量。原因是在我的应用程序中，所有这些类都用作 'namespaces'。为了解决 'issue'，我将 A 继承的部分替换为自身的副本（伪代码）：

class A:
    a = 1

class B(A):  # B.a resolves to A.a
    pass

class C(A):  # C.a resolves to A.a
    c = 3

copy_func(B.A, A)  # investigates public attrs of A and B and create copies, now B.a is not A.a
copy_func(C.A, A)  # investigates public attrs of A and B and create copies, now C.a is not A.a

Answer 1

定义 __init_subclass__ 以在定义子类时自动复制超类属性。

import copy

class A:
    a = []

    def __init_subclass__(cls, **kwargs):
        for base in cls.mro():
            for attr in base.__dict__:
                if attr not in cls.__dict__ and not attr.startswith("_"):
                    setattr(cls, attr, copy.copy(getattr(cls, attr)))

这将从超类命名空间中复制所有不以 _ 开头的内容。在实践中，人们可能希望应用更严格的规则。

定义子类时__init_subclass__自动运行。这意味着子类无需运行显式编码即可获得复制的属性。

class B(A):
    pass

class C(A):
    c = 3

assert B.a is not A.a
assert C.a is not A.a

Python：确保 class 属性不在公共继承树之间共享

Python: ensure class attributes are not shared between common inheritance trees

python

inheritance