__base__不起作用！下一步是什么? [英] __bases__ doesn't work! What's next?

问题描述

以下代码在Python 3.x中不起作用，但它曾经与旧式类一起工作:

The following code doesn't work in Python 3.x, but it used to work with old-style classes:

class Extender:
    def extension(self):
        print("Some work...")

class Base:
    pass

Base.__bases__ += (Extender,)

Base().extension()

问题很简单: 如何在运行时动态地将超类添加到Python 3.x中的类?

但是我已经准备好答案了！ )

But I'm ready the answer will be hard! )

推荐答案

似乎可以动态更改Base.__bases__ 如果Base.__base__不是object. (通过动态更改，我的意思是，从Base继承的所有现有实例也将动态更改.否则，请参见

It appears that it is possible to dynamically change Base.__bases__ if Base.__base__ is not object. (By dynamically change, I mean in such a way that all pre-existing instances that inherit from Base also get dynamically changed. Otherwise see Mykola Kharechko's solution).

如果Base.__base__是某个虚拟类TopBase，则分配给Base.__bases__似乎可行:

If Base.__base__ is some dummy class TopBase, then assignment to Base.__bases__ seems to work:

class Extender(object):
    def extension(self):
        print("Some work...")

class TopBase(object):
    pass

class Base(TopBase):
    pass

b=Base()
print(Base.__bases__)
# (<class '__main__.TopBase'>,)

Base.__bases__ += (Extender,)
print(Base.__bases__)
# (<class '__main__.TopBase'>, <class '__main__.Extender'>)
Base().extension()
# Some work...
b.extension()
# Some work...

Base.__bases__ = (Extender, TopBase) 
print(Base.__bases__)
# (<class '__main__.Extender'>, <class '__main__.TopBase'>)
Base().extension()
# Some work...
b.extension()
# Some work...

经过测试可以在Python 2(适用于新旧类)和Python 3中运行.我不知道为什么它可以运行，而不能运行:

This was tested to work in Python 2 (for new- and old-style classes) and for Python 3. I have no idea why it works while this does not:

class Extender(object):
    def extension(self):
        print("Some work...")

class Base(object):
    pass

Base.__bases__ = (Extender, object)
# TypeError: __bases__ assignment: 'Extender' deallocator differs from 'object'

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