为什么类中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}

我实例化该类的一个对象，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而不更改为7?

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

推荐答案

您在调用构造函数时创建了字典.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的，而是通过值传递的.

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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