类型错误:描述符“__weakref__"不适用于来自父 __str__ 方法的对象 [英] TypeError: descriptor '__weakref__' doesn't apply to object from parent __str__ method

问题描述

我有一个父类，我们称之为A和一堆子类，B、C、D 等我想在父类上定义一个 __str__() 方法，在它里面我想通过 dir(self).它有效，但是当我使用 callable(getattr(self, attr)) 检查名称是否可调用时，我得到:

I have a parent class, let's call it A and a bunch of child classes, B, C, D, etc. I want to define a single __str__() method on the parent class and inside it I want to access the members of the child class via dir(self). It works, but when I check if the name is a callable with callable(getattr(self, attr)) I get:

TypeError: 'A' 对象的描述符 '__weakref__' 不适用于 'B' 对象

TypeError: descriptor '__weakref__' for 'A' objects doesn't apply to 'B' object

引发错误的代码是这样的:

The code that raises the error is this:

[attr for attr in dir(self) if not callable(getattr(self, attr)) 而不是 attr.startswith("__")]

谁能解释一下这是什么意思?

Can someone explain what does it mean?

旁注:我设法让所有班级成员通过 self.__dict__ 循环，我的问题只是出于好奇，因为我无法理解错误.

Sidenote: I managed to get all class members cycling through self.__dict__, my question is just out of curiosity, since I cannot understand the error.

编辑

我做了一个更简单的代码版本:

I made a simpler version of the code:

class A():

    def __init__(self):
        pass

    def test(self, par):
        print('10')

    def __str__(self):
        members = [attr for attr in dir(self) if not callable(getattr(self, attr)) and not attr.startswith("__")]

        str = ''
        for m in members:
            str += m
            str += ','

        return str

class B(A):

    def test_b(self, par):
        print('10_b')

    def __init__(self,first,second):
        self.first = first
        self.second = second

if __name__ == '__main__':   
    b = B('one', 'two')
    print(b)

但是这里的代码可以正常工作并正确打印first,second,

But here the code works and correctly prints first,second,

原始代码被打包，A 和 B 的等价物在一个单独的包中，由主"脚本调用.实际代码中该类的 __str__() 方法中的相同代码引发错误.

The original code is packaged, with the equivalent of A and B in a separate package that is called by a "main" script. The same code in the __str__() method of the class in the actual code raises the error.

推荐答案

您的代码发生了一些非常奇怪的事情.如果有机会发现问题，您将需要提供更多详细信息.您引用的错误仅在一处引发(此处a>) -- 在一种防止来自一个类(如 __weakref__)的描述符被用于另一种不兼容类型的方法中.

There is something very funky is going on with your code. You'll need to give a lot more detail if there's any chance of finding the problem. The error you reference is raised in one place only (here) -- in a method that protects against descriptors from one class (like __weakref__) from being used on another incompatible type.

我可以重现错误(并有 B 子类 A)的唯一方法是这样的:

The only way I could reproduce the error (and have B subclass A) was like this:

class A:
    pass

class Z:
    pass

class B(A,Z):
    pass

B.__weakref__.__get__(A()) # works
B.__weakref__.__get__(Z()) # fails

# because
assert B.__weakref__ == A.__weakref__ # is true
assert B.__weakref__ == Z.__weakref__, 'B uses A.__weakref__ rather than  Z.__weakref__'

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