Python 设计模式创建型单例模式

class Singleton(object):

    _instance = None

    def __new__(cls, *args, **kwargs):
        if cls._instance is None:
            cls._instance = object.__new__(cls, *args, **kwargs)
        return cls._instance

if __name__ == '__main__':
    instance1 = Singleton()
    instance2 = Singleton()
    instance3 = Singleton()

    # 打印出 3 个实例对象的内存地址，判断是否相同。
    print(id(instance1))
    print(id(instance2))
    print(id(instance3))

def singleton(cls):

    _instance = {}

    def _singleton(*args, **kargs):
        if cls not in _instance:
            _instance[cls] = cls(*args, **kargs)
        return _instance[cls]

    return _singleton

@singleton
class Singleton(object):
    """单例实例"""

    def __init__(self, arg1):
        self.arg1 = arg1

if __name__ == '__main__':
    instance1 = Singleton("xag")
    instance2 = Singleton("xingag")

    print(id(instance1))
    print(id(instance2))

class Singleton(object):

    _instance = None
    _instance_lock = threading.Lock()

    def __new__(cls, *args, **kwargs):
        if cls._instance is None:
            with cls._instance_lock:
                cls._instance = object.__new__(cls, *args, **kwargs)
        return cls._instance

def task(arg):
    instance = Singleton()
    print(id(instance), '\n')

if __name__ == '__main__':
    for i in range(3):
        t = threading.Thread(target=task, args=[i, ])
        t.start()