python singleton 4种单例

def singleton(cls, *args, **kwargs):

    instances = {}

    def inner(cls, *args, **kwargs):

        if cls not in instances:

            instances[cls] = cls(*args, **kwargs)

        return instances[cls]

    return inner

@singleton

class Test1:

    pass

# 推荐使用这种 简单好用 线程安全

# ===========================================================

import threading

class Singleton:

    def __init__(self, cls):

        self.__cls = cls

        self.__instance = None

        self._lock = threading.Lock()

    def __call__(self, *args, **kwargs):

        self._lock.acquire()

        if self.__instance is None:

            self.__instance = self.__cls(*args, **kwargs)

        self._lock.release()

        return self.__instance

@Singleton

class Test2:

    pass

# 继承时的执行顺序 base new -> son new -> son init. new 相当于构造方法，init相当于实例后再初始化 先执行父类的new 就好比先是人再是学生

# ==============================================================

class SingleBase(object):

    instance = None

    def __new__(cls, *args, **kwargs):

        # if not instance:

        #     instance = cls.__new__(*args, **kwargs):

        # return instance

        if cls.instance is None:

            cls.instance = object.__new__(cls)

        return cls.instance

    def __init__(self):

        pass

class Test3(SingleBase):

    def __init__(self, name):

        self._name = name

    def get_name(self):

        return self._name

# meta 这个我还不是很懂

# =====================================================

class MetaSingleton(type):

    _instances = {}

    def __call__(cls, *args, **kwargs):

        if cls not in cls._instances:

            cls._instances[cls] = super().__call__(*args, **kwargs)

        return cls._instances[cls]

class Test4(metaclass=MetaSingleton):

    def __init__(self):

        pass

if __name__ == '__main__':

    t1 = Test3('jwang')

    t2 = Test3('hello')

    print(id(t1))

    print(id(t2))

    print(t1.get_name())

    print(t2.get_name())

    test3 = Test4()

    test4 = Test4()

    print(id(test3) == id(test4))
巴特西

python singleton 4种单例

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