bases 不起作用！接下来是什么？

发布于 2024-09-08 03:57:48 字数 309 浏览 7 评论 0原文

以下代码在 Python 3.x 中不起作用，但它曾经适用于旧式类：

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

class Base:
    pass

Base.__bases__ += (Extender,)

Base().extension()

问题很简单： 如何动态（在运行时）添加超类Python 3.x 中的类？

但我已经准备好答案将是困难的！）

原文

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()

Question is simple: How can I add dynamically (at runtime) a super class to a class in Python 3.x?

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

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情话难免假 2024-09-15 03:57:48

看来可以动态更改Base.__bases__
如果Base.__base__不是object。（动态更改是指从 Base 继承的所有预先存在的实例也会动态更改。否则请参阅 Mykola Kharechko 的解决方案）。

如果 Base.__base__ 是某个虚拟类 TopBase，那么对 Base.__bases__ 的赋值似乎可以工作：经过

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...

测试，可以在 Python 2 中工作（对于新式和旧式类）和Python 3。我不知道为什么它可以工作，而这却不能：

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'

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).

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...

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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浴红衣 2024-09-15 03:57:48

对于我来说这是不可能的。但您可以动态创建新类：

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

class Base(object):
    pass

Base = type('Base', (Base, Extender, object), {})
Base().extension()

As for me it is impossible. But you can create new class dynamically:

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

class Base(object):
    pass

Base = type('Base', (Base, Extender, object), {})
Base().extension()

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