python - Python 类属性可以添加吗？

Question

我有一个具有以下类结构的项目：

class A(object):
    elems = [1, 2, 3]

class B(A):
    pass

class C(B):
    elems = [20, 100]

class D(B):
    elems = [4, 5]

目前，Python 的默认继承行为是elems在每个后​​续属性声明中覆盖该属性，例如：

A.elems == [1, 2, 3]
B.elems == [1, 2, 3]
C.elems == [20, 100]
D.elems == [4, 5]

我希望能够访问这些值的附加列表。换句话说，我希望能够检索以下列表：

A.collated() == [1, 2, 3]
B.collated() == [1, 2, 3]
C.collated() == [1, 2, 3, 20, 100]
D.collated() == [1, 2, 3, 4, 5]

我不知道该怎么做。任何帮助将不胜感激。

在此先感谢，
-B

Answer 1

这里最简单的解决方案是明确：

class A(object):
    elems = [1, 2, 3]
    @classmethod
    def collated(cls):
      return sorted(cls.elems)

class B(A):
    pass

class C(B):
    elems = B.elems + [20, 100]

class D(B):
    elems = B.elems + [4, 5]

print "A.collated() == ", A.collated()
print "B.collated() == ", B.collated()
print "C.collated() == ", C.collated()
print "D.collated() == ", D.collated()

你可以做一些棘手的事情来让它更加自动化，但我认为你不想这样做。（如果您认为需要，请先阅读描述符或元类的工作原理，然后再提出具体问题。）

Answer 2

只需明确并访问您要扩展的父级的类实例......

class A(object):
    elems = [1, 2, 3]

class B(A):
    elems = A.elems # or pass

class C(B):
    elems = B.elems + [20, 100]

class D(B):
    elems = B.elems + [4, 5]

print A.elems, B.elems, C.elems, D.elems
# [1, 2, 3] [1, 2, 3] [1, 2, 3, 20, 100] [1, 2, 3, 4, 5]