动态添加/覆盖property属性的setter和getter

我需要使用/模仿语法糖语法在子类中动态装饰 getter 和 setter 对方法。

我正在努力解决 setter 的实现问题。

class A:

    def __init__(self, x):
        print('init')
        self.__x = x

    @property
    def x(self):
        print('getter')
        return self.__x

    @x.setter
    def x(self, v):
        print('setter')
        self.__x = v


class Dec:
    def __init__(self):
        print('init - dec')

    def __call__(self, cls):
        c = type('A_Dec', (cls,), {})
        # super-init
        setattr(c, '__init__', lambda sub_self, x: super(type(sub_self), sub_self).__init__(x))
        # getter
        setattr(c, 'x', property(lambda sub_self: super(type(sub_self), sub_self).x))
        
        # setter - see below

        return c

dec_A = Dec()(A)
dec_a = dec_A('p')
print(dec_a.x)

Output

init - dec
init
getter
p

如果我尝试实现 setter 方法Dec, dec_a.x = 'p'，通过以下方法我收集了以下错误：

    # setter-statements of __call__

    # Attempt 1
    setattr(c, 'x', property(fset=lambda sub_self, v: super(type(sub_self), sub_self).x(v)))
    # AttributeError: unreadable attribute
    
    # Attempt 2 - auxiliary function
    def m(sub_self, v):
       print('--> ', sf, super(type(sub_self), sub_self))
       super(type(sub_self), sub_self).x = v
    
    # Attempt 2.A
    setattr(c, 'x', eval('x.setter(m)'))
    # NameError: name 'x' is not defined
    
    # Attempt 2.B
    setattr(c, 'x', property(fset=lambda sf, v: m(sf, v)))
    # AttributeError: unreadable attribute
    
    # Attempt 2.C: !! both at once, `fget`and `fset` so, in case, comment the getter in the above code to avoid conflicts
    setattr(c, 'x', property(fget=lambda sub_self: super(type(sub_self), sub_self).x, fset=m))
    # AttributeError: 'super' object has no attribute 'x'
    
    # Attempt 2.D
    p = property(fget=lambda sub_self: super(type(sub_self), sub_self).x, fset=m)
    setattr(c, 'x', p)
    # AttributeError: 'super' object has no attribute 'x'

尝试1引发错误，因为（我猜）用括号设置属性。所以在尝试2我使用了辅助功能，因为lambda不允许初始化、'='语句，同样没有成功。

• 有没有办法动态模仿属性 getter/setter 装饰器？ （可能不需要额外的进口） 还有其他方法吗？

• 额外：为什么 super 没有属性就不起作用？super().x(v) -> TypeError: super(type, obj): obj must be an instance or subtype of type

EDIT:

• 额外的答案：来自文档：零参数形式仅适用于类定义内部[...]
• 使用 python3.9

属性设置器未正确设置。为了形象化这一点，如果没有为属性显式设置 setter，则该属性将变为只读，如下所示有记录的 https://docs.python.org/3/library/functions.html#property.

class Parrot:
    def __init__(self):
        self._voltage = 100000

    @property
    def voltage(self):
        """Get the current voltage."""
        return self._voltage

@property 装饰器将Voltage()方法变成了一个“getter”只读属性同名

假设我们有这个：

class A:
    def __init__(self, x):
        self.__x = x

    @property
    def x(self):
        return self.__x

a = A(123)

print(a.x)  # will display "123"
a.x = 456  # will display "AttributeError: can't set attribute"

在原始代码中，您创建了一个新类型A_Dec。您明确设置了 getter：

# getter
setattr(c, 'x', property(lambda sub_self: super(type(sub_self), sub_self).x))

但是您没有明确设置任何设置器，因此使得x属性只读。这会导致此代码出现错误：

dec_a.x = 'new value!'  # will display "AttributeError: can't set attribute"

解决方案1

不要明确定义 getter。这样，所有访问x将被委托给实际班级A.

解决方案2

如果定义了 getter，那么还要定义 setter。

...
class Dec:
    ...
    def __call__(self, cls):
        ...
        # setter
        x_property = getattr(c, 'x')
        x_setter = getattr(x_property, 'setter')
        setattr(c, 'x', x_setter(lambda sub_self, v: super(type(sub_self), type(sub_self)).x.fset(sub_self, v)))
        ...
...

• The usage of c.x.setter is as documented https://docs.python.org/3/library/functions.html#property:

  一个属性对象有getter, setter, and deleter可用作装饰器的方法

• The usage of .fset is as documented https://docs.python.org/3/library/functions.html#property:

  fset是一个设置属性值的函数...返回的属性对象也有属性fget, fset, and fdel对应于构造函数参数。

所以添加以下几行就会成功：

dec_a.x = 'new value!'
print(dec_a.x)

Output:

setter
getter
new value!

更多参考：

• https://newbedev.com/how-to-call-a-property-of-the-base-class-if-this-property-is-being-overwriting-in-the-driven-class https://newbedev.com/how-to-call-a-property-of-the-base-class-if-this-property-is-being-overwritten-in-the-derived-class
• https://gist.github.com/Susensio/979259559e2bebcd0273f1a95d7c1e79 https://gist.github.com/Susensio/979259559e2bebcd0273f1a95d7c1e79