Python-从其他内部类引用内部类 [英] Python - reference inner class from other inner class

问题描述

我正在尝试从另一个内部类中引用一个内部类.我都尝试过:

I am trying to reference an inner class from another inner class. I have tried both :

class Foo(object):

  class A(object):
    pass

  class B(object):
    other = A

和

class Foo(object):

  class A(object):
    pass

  class B(object):
    other = Foo.A

具有相应结果:

Traceback (most recent call last):
  File "python", line 1, in <module>
  File "python", line 6, in Foo
  File "python", line 7, in B
NameError: name 'A' is not defined

和

Traceback (most recent call last):
  File "python", line 1, in <module>
  File "python", line 6, in Foo
  File "python", line 7, in B
NameError: name 'Foo' is not defined

这可能吗?

推荐答案

这是不可能的，因为您在类中定义的所有内容仅在该类的实例中才成为有效成员，除非您使用@staticmethod定义方法，但类没有此类属性.

This is not possible, since everything you define in a class becomes a valid member only in an instance of that class, unless you define a method with @staticmethod, but there is no such property for a class.

因此，这也不起作用:

class Foo(object):
    x = 10

    class A(object):
        pass

    class B(object):
        other = x

此可以起作用，但这不是您想要的:

This will work, but it is not what you intended:

class Foo(object):
  x = 10

  class A(object):
    pass

  class B(object):
    def __init__(self):
        self.other = Foo.A

f = Foo()
print(f.B().other)

输出为:

<class '__main__.Foo.A'>

之所以可行，是因为在创建对象时会评估方法(在本例中为__init__)，而在读取和解释类时会评估__init__之前的赋值.

The reason this works is that the methods (in this case __init__) are evaluated when the object is created, while assignment before the __init__ are evaluated while the class is read and interpreted.

只需在自己的模块中定义所有类，就可以得到与您想要的相同的东西.导入模块，使其成为对象，其字段是您在其中定义的类.

You can get about the same thing you want by simply define all the classes inside a module of their own. The importing the module, makes it an object whose fields are the classes you define in it.

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