更改实例方法中的类实例 [英] Change class instance inside an instance method

问题描述

任何想法如果有办法让以下代码工作

Any idea if there is a way to make the following code to work

class Test(object):

    def __init__(self, var):
        self.var = var

    def changeme(self):
        self = Test(3)

t = Test(1)
assert t.var == 1
t.changeme()
assert t.var == 3

类似于以下可以安全地用于更复杂的对象（如django模型，热插拔实例引用的数据库条目） p>

is something like the following safe to use for more complex objects (like django models, to hot swap the db entry the instance is referring to)

class Test(object):

    def __init__(self, var):
        self.var = var

    def changeme(self):
        new_instance = Test(3)
        self.__dict__ = new_instance.__dict__

t = Test(1)
assert t.var == 1
t.changeme()
assert t.var == 3

推荐答案

self = Test（3）是重新绑定本地名称 self ，没有外部可观察的效果。

self = Test(3) is re-binding the local name self, with no externally observable effects.

分配 self .__ dict __ （除非你在谈论具有 __ slots __ 或来自具有非平凡元类的类的实例）通常是正确的，因此 self .__ init __（3 ）重新初始化实例。但我更喜欢有一个特定的方法 self.restart（3）其中知道它在一个已经初始化的实例上调用，需要满足这种特殊和不寻常的情况。

Assigning self.__dict__ (unless you're talking about instances with __slots__ or from classes with non-trivial metaclasses) is usually OK, and so is self.__init__(3) to re-initialize the instance. However I'd prefer to have a specific method self.restart(3) which knows it's being called on an already-initialized instance and does whatever's needed to cater for that specific and unusual case.

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