Python - 类实例共享类字典变量？ [复制]答案

【问题标题】：Python - Class instances share class dictionary variable? [duplicate]Python - 类实例共享类字典变量？ [复制]
【发布时间】：2018-11-11 07:41:24
【问题描述】：

class Student():

    NAME = ''
    DICT = {}

    def __init__(self, name):
        self.NAME = name
        self.DICT['name'] = name

    def change_DICT(self, change):
        self.DICT['name'] = change


student_one = Student('Leo')
student_two = Student('Liz')

print ('Student one NAME: ' + student_one.NAME)
print ('Student two NAME: ' + student_two.NAME)
print ('---------------------------------')
print ('Student one DICT: ' + str(student_one.DICT))
print ('Student two DICT: ' + str(student_two.DICT))
print ('---------------------------------')
student_one.change_DICT('Tom')
print ('Student one DICT: ' + str(student_one.DICT))
print ('Student two DICT: ' + str(student_two.DICT))


>> Student one NAME: Leo
>> Student two NAME: Liz
>> ---------------------------------
>> Student one DICT: {'name': 'Liz'}
>> Student two DICT: {'name': 'Liz'}
>> ---------------------------------
>> Student one DICT: {'name': 'Tom'}
>> Student two DICT: {'name': 'Tom'}

我已经玩了几个小时了，但仍然无法理解它。更改Student 类的一个实例的DICT 如何同步更改所有其他实例的DICT。

这是怎么发生的？如果我真的需要使用dict，解决这个问题的最佳方法是什么？

【问题讨论】：

除了我的回答：我确实觉得很奇怪self.DICT 仍然可以针对该类变量，所以我不确定为什么会发生这种情况。也许其他人可以启发我们。
@BramVanroy self.DICT 不针对该类变量，但 self.DICT['name'] 可以。即使使用预定义的DICT，您的代码也能正常工作。谢谢你的帮助！我会将此标记为重复，因为我在@Cyber Tailor 建议的帖子中找到了我需要的内容。

标签： python-3.x class dictionary instance instance-variables

【解决方案1】：

您可以通过更改DICT 和NAME 等类属性的初始化位置来实现所需的输出。我给你举个例子。

class Student():


    def __init__(self, name):
        self.DICT = {}
        self.NAME = name
        self.DICT['name'] = name

    def change_DICT(self, change):
        self.DICT['name'] = change

student_one = Student('Leo')
student_two = Student('Liz')

print ('Student one NAME: ' + student_one.NAME)
print ('Student two NAME: ' + student_two.NAME)
print ('---------------------------------')
print ('Student one DICT: ' + str(student_one.DICT))
print ('Student two DICT: ' + str(student_two.DICT))
print ('---------------------------------')
student_one.change_DICT('Tom')
print ('Student one DICT: ' + str(student_one.DICT))
print ('Student two DICT: ' + str(student_two.DICT))

这将给出如下输出：

Student one NAME: Leo
Student two NAME: Liz
---------------------------------
Student one DICT: {'name': 'Leo'}
Student two DICT: {'name': 'Liz'}
---------------------------------
Student one DICT: {'name': 'Tom'}
Student two DICT: {'name': 'Liz'}

在这里，您将检查字典值是否已更改。

【讨论】：

【解决方案2】：

您正在混合类变量和实例变量。当你在构造函数之外声明一个变量时（即上面__init__)它是一个类变量，意味着它是共享的。相反，你只需要实例变量，如下所示。

class Student():
    def __init__(self, name):
        self.NAME = name
        self.DICT = {'name': name}

    def change_DICT(self, change):
        self.DICT['name'] = change


student_one = Student('Leo')
student_two = Student('Liz')

print ('Student one NAME: ' + student_one.NAME)
print ('Student two NAME: ' + student_two.NAME)
print ('---------------------------------')
print ('Student one DICT: ' + str(student_one.DICT))
print ('Student two DICT: ' + str(student_two.DICT))
print ('---------------------------------')
student_one.change_DICT('Tom')
print ('Student one DICT: ' + str(student_one.DICT))
print ('Student two DICT: ' + str(student_two.DICT))

【讨论】：