如何使类不可变在python？ [英] How to make class immutable in python?

问题描述

我在这里阅读了很多关于这个主题，但我还是找不到一个合适的答案。
我有一个类如下：

I have read a lot about this subject here but i still can't find an appropriate answer. I have a class like:

class A(object):

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

    def __eq__(self, other):
        return ****

    def __str__(self):
        return *****

    def __repr__(self):
        return **** 

a = A("a", "b")

a.first =cfor example？

How can i forbid a.first = "c" for example ?

推荐答案

您可以覆盖 __ setattr __ 以防止任何更改：

You can override __setattr__ to either prevent any changes:

def __setattr__(self, name, value):
    raise AttributeError('''Can't set attribute "{0}"'''.format(name))

或阻止添加新属性：

def __setattr__(self, name, value):
    if not hasattr(self, name):
        raise AttributeError('''Can't set attribute "{0}"'''.format(name))
    # Or whatever the base class is, if not object.
    # You can use super(), if appropriate.
    object.__setattr__(self, name, value)

$ c> hasattr 对允许的属性列表进行检查：

You can also replace hasattr with a check against a list of allowed attributes:

if name not in list_of_allowed_attributes_to_change:
    raise AttributeError('''Can't set attribute "{0}"'''.format(name))

---

另一种方法是使用属性而不是纯属性：

---

Another approach is to use properties instead of plain attributes:

class A(object):

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

    @property
    def first(self):
        return self._first

    @property
    def second(self):
        return self._second

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