为什么类内字典中的属性值不引用该类的相同属性? [英] why doesn't an attribute value in a dictionary within a class refer to the same attribute of the class?

问题描述

class test(object): 
    def __init__(self): 
        self.a = 5 
        self.d = {'alfa': self.a}

我实例化类的一个对象，并为其分配一个新值:

I instantiate an object of the class, and assign a new value to it:

a_test = test()
a_test.a = 7

为什么 a_test.d['alfa'] 保持 5 而不是变成 7?

Why does a_test.d['alfa'] remain 5 and not change to 7?

推荐答案

在调用构造函数时创建字典.因此，字典中的值是在构造过程中设置的 - 它们不是通过引用传递，而是通过值传递.

You create the dictionary when you call the constructor. Therefore the values in the dictionary are set during construction - they aren't passed by reference, but rather by value.

字典中的值指向传入的对象的值，而不是对象本身.因此，简单地将 self.a 作为值并不会自动更新字典，除非 self.a 是可变的(例如列表).

The values in the dictionary point to value of the object that is passed in, but not the object itself. So simply having self.a as a value doesn't automatically update the dictionary, unless self.a is mutable (eg. a list).

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