Python3 Singleton元类方法不起作用 [英] Python3 Singleton metaclass method not working

问题描述

我看到了许多在Python中制作单例的方法，并且尝试在Python 3.2(Windows)中使用元类实现，但似乎并没有返回我的单例类的相同实例.

I saw a lot of methods of making a singleton in Python and I tried to use the metaclass implementation with Python 3.2 (Windows), but it doesn"t seem to return the same instance of my singleton class.

class Singleton(type):
    _instances = {}
    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
        return cls._instances[cls]

class MyClass(object):
    __metaclass__ = Singleton

a = MyClass()
b = MyClass()
print(a is b) # False

我现在使用的装饰器实现正在运行，但是我想知道该实现有什么问题吗?

I use the decorator implementation now which is working, but I'm wondering what is wrong with this implementation?

推荐答案

元类语法已更改在Python3中.请参阅文档说明.

The metaclass syntax has changed in Python3. See the documentaition.

class MyClass(metaclass=Singleton):
    pass

它有效:

>>> MyClass() is MyClass()
True

这篇关于Python3 Singleton元类方法不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！