如何防止在 class 之外重新分配 class 方法？

Question

我希望我的某些 class 方法不能在 class 的外部（或外部和内部）重新分配。 A的函数在python中也是对象，是否可以实现我想要的？这是方法；

def x(self):
    """Return x, the horizontal distance between the shape and the leftmost
    of the screen, in pixels.
    """
    return self.__x

现在在class之外，很容易搞砸这个方法；

shape = Shape(10, 20)
shape.x = 30
print(shape.x)  # Prints 30
print(shape.x())  # TypeError: 'int' object is not callable

是否可以防止这种 class 方法的赋值？

Answer 1

使 x 成为属性而没有 setter，而不是方法。

class Shape:
    ...

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

尝试分配给 x 将导致异常：

>>> shape.x = 30
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't set attribute

如果您确实想要必须调用的东西，请使用属性 return 代替函数将要调用的值 return.

class Shape:

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

Answer 2

例如，您可以覆盖 __setattr__ 方法来检查密钥是否在禁止列表中...

class Shape:
    def __init__(self, a, b):
        self.__x = a
        self.__y = b

    def x(self):
        return self.__x

    def __setattr__(self, key, value):
        if key in ('x', 'y'):
            raise TypeError(f"You can't change {key}")
        super(Shape, self).__setattr__(key, value)


shape = Shape(11, 20)
shape.z = 100  # OK
print(shape.z)
print(shape.x())
shape.x = 30  # raise an exception

注意：正如@Chepner 指出的那样，重写 __setattr__ 只是阻止您通过赋值语句更改 x 的值，而不是更改它根本。喜欢 object.__setattr__(shape, 'x', 30)

如何防止在 class 之外重新分配 class 方法？

How to prevent re-assignment of a class method outside the class?

python

oop

methods

class

python-3.x