在派生类中访问基类属性-在“类范围"中. [英] Access base class attribute in derived class - in "class scope"

问题描述

class Outer(object):
    class InnerBase(object): _var = {'foo', 'bar'}
    class Derived(InnerBase):
        _var = _var | {'baz'} # NameError: name '_var' is not defined
        _var = InnerBase._var | {'baz'} #  name 'InnerBase' is not defined
        _var = Outer.InnerBase._var | {'baz'} #  free variable 'Outer'
        # referenced before assignment in enclosing scope

在Outer中移动_var无济于事-在模块范围内移动_var可以工作，但无法达到创建类的目的.那么如何解决呢?

Moving _var in Outer does not help - moving it in module scope would work but defeats the purpose of having classes. So how to go about that ?

来自Java，所以类的作用域规则对我来说是一个头疼的问题-简要地介绍一下.顺便说一句:

coming from Java so the scoping rules of classes are a head scratcher for me - a briefing would be appreciated. This works btw:

    class Derived(InnerBase): pass
    Derived._var = InnerBase._var | {'baz'}

但这不是优雅的顶峰.

相关:嵌套类的作用域?-但是在这里，我们特别想访问父类类(而不是外部类型)

Related: Nested classes' scope? - but here we specifically want to access our parent class (rather than the Outer type)

我实际上所追求的是类似_var = __class__._var的语法(或hack)，或者是关于为什么不存在的解释

What I am actually after is a _var = __class__._var-like syntax (or hack), or an explanation as to why it's not there

推荐答案

您可以绕过class语句并使用对type的显式调用.

You can bypass the class statement and use an explicit call to type.

class Outer(object):
    class InnerBase(object): _var = {'foo', 'bar'}
    Derived = type('Derived',
                   (InnerBase,),
                   {'_var': InnerBase._var | {'baz'}}
                  )

之所以可行，是因为未通过定义Derived的class语句中的赋值语句来设置Derived._var，而是从您在与InnerBase本身相同的环境中创建的字典中导入的.

This works because Derived._var is not being set via an assignment statement in the class statement defining Derived, but is imported from a dictionary you create in the same environment as InnerBase itself.

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