如何区分 class 内部和 class 外部设置为 _setattr 的属性？

Question

在 __setattr__() 中有什么方法可以区分来自 class 或 child/inheriting class 内部的属性集和来自当前外部的属性集或 child class?

我想从 "outside" 更改设置属性的工作方式，在我制作模块的情况下，我希望用户在设置属性时与在 [= 内部设置属性时具有不同的逻辑27=].

例如：
当从 class 中调用时 i.x = 5 应该正常分配 5 并且 i 是它的一个实例，但是当从另一个 class 中调用时它应该减去 5 而不是设置为 5。

Answer 1

一个解决方案可能是始终在 class 中使用 self.__dict__，而不调用 __setattr__ 方法。

示例：

class myClass:

    def __init__(self, value):
        self.__dict__['a'] = value

    def __setattr__(self, name, value):
        print("called from outside")
        if name == 'a':
            self.__dict__[name] = value - 5
        else:
            self.__dict__[name] = value


f = myClass(10)

print(f.a)
# 10

f.a = 20
print(f.a)
# called from outside
# 15

Answer 2

有点低级，但你可以使用 inspect 模块：

import inspect

class A:

    def __init__(self):
        self.__x = 0

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

    @x.setter
    def x(self, value):
        f = inspect.currentframe()
        if 'self' in f.f_back.f_locals and issubclass(type(f.f_back.f_locals['self']), A):
            print('Called from class!')
            self.__x = -value
        else:
            print('Called from outside!')
            self.__x = value

    def fn(self):
        print('Calling A.x from inside:')
        self.x = 10

class B(A):
    def __init__(self):
        super().__init__()

    def fn2(self):
        print('Calling B.x from inside:')
        self.x = 15

a = A()
print("A.x after init:", a.x)
print('Calling A.x from outside')
a.x = 10
print("A.x called from the outside:", a.x)
a.fn()
print("A.x called from the inside:", a.x)

b = B()
print("B.x after init:", b.x)
print('Calling B.x from outside')
b.x = 20
print("B.x called from the outside:", b.x)
b.fn2()
print("B.x called from the inside:", b.x)

打印：

A.x after init: 0
Calling A.x from outside
Called from outside!
A.x called from the outside: 10
Calling A.x from inside:
Called from class!
A.x called from the inside: -10
B.x after init: 0
Calling B.x from outside
Called from outside!
B.x called from the outside: 20
Calling B.x from inside:
Called from class!
B.x called from the inside: -15

Answer 3

使用属性。在 class 内部，您可以直接分配给底层属性。在外部，对 x 的赋值反而会递减它。

class Foo:
    def __init__(self):
         self._x = 0

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

    @x.setter
    def x(self, value):
        self._x -= value

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如何区分 class 内部和 class 外部设置为 _setattr 的属性？

How to differentiate between a property being set with _setattr from inside the class and outside the class?