从另一个嵌套类访问属性

Question

I would like to achieve something similar to this construction:

class Outer:
    class A:
        foo = 1

    class B:
        def __init__(self):
            self.bar = A.foo

Outer.B().bar  # ==> 1

But this fails with

NameError: name 'A' is not defined

I'm not even sure I understand why as A is (I thought) in scope.

Could you help me clarify why this doesn't work and how I could get around it?

Answer 1

Names are looked up only in globals , locals , and nonlocal cells (but you don't have a closure here).

Write Outer.A instead of A , or consider making Outer a module.

Answer 2

如果您使用Outer.A.foo它将起作用。

Answer 3

就像您对Outer.B().bar所做的操作一样：对self.bar=Outer.A().foo也做相同的self.bar=Outer.A().foo

Answer 4

Inner classes in Python do not have acces to the members of the enclosing class. A is not in scope of B as you state. A and B are both in scope of Outer, but they do not know of each other. Therefore a possible solution to your problem:

class Outer:
    class A:
        foo = 1

    class B:
        def __init__(self, class_a):
            self.bar = class_a.foo

    def __init__(self):
        self.a = self.A()
        self.b = self.B(self.a)


print(Outer.A.foo) # 1
print(Outer.B.bar) # AttributeError: type object 'B' has no attribute 'bar'

outer = Outer()
print(outer.a.foo)  # 1
print(outer.b.bar)  # 1