列表中的 Python 属性 [英] Python property on a list

问题描述

我是 Python 新手，我刚刚发现了这些属性.当我在一个简单的变量上尝试它时它工作得很好，但我不能让它在列表上工作.执行下面的代码时，它将调用两次 getter 而不是 setter.我知道在我的例子中，属性没有附加值，但它是为了简化.

I am new to Python and I just discovered the properties. It works just fine when I try it on a simple variable but I cannot make it work on a list. When executing the code below it will call two times the getter and not the setter. I know that in my example the property has no added value but it is to simplify.

class C:
    def __init__(self):
        self._x = [1, 2, 3]

    @property
    def x(self):
        print("getter")
        return self._x
    @x.setter
    def x(self, value):
        print("setter")
        self._x = value

c = C()
c.x[1] = 4
print(c.x[1])

有人知道我做错了什么吗?

Does anybody have an idea about what I'm doing wrong ?

推荐答案

setter/getter 仅在直接获取或设置属性时使用:

The setter/getter are only used if you directly get or set the property:

c.x           # getter
c.x = [1,2,3] # setter

如果您修改属性中的元素，则会获取该属性，然后设置相应的元素.你的例子相当于

If you modify an element in the property you get the property and then set the corresponding element. Your example is equivalent to

d = c.x       # getter again
d[1] = 4

您也可以使用 __getitem__ 和 __setitem__ 直接允许设置和获取特定项目.

You could also use __getitem__ and __setitem__ to directly allow setting and getting specific items.

class C:
    def __init__(self):
        self._x = [1, 2, 3]

    @property
    def x(self):
        print("getter")
        return self._x
    @x.setter
    def x(self, value):
        print("setter")
        self._x = value

    def __getitem__(self, idx):
        print("getitem")
        return self._x[idx]

    def __setitem__(self, idx, value):
        print("setitem")
        self._x[idx] = value

>>> c = C()
>>> c[1] = 3
setitem
>>> c.x
getter
[1, 3, 3]
>>> c[2]
getitem
3

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