[Python知识库]python单例模式

class Single(object):

    def __init__(self, cfg):
        cfg = dotdict(cfg)
        self.bootstrap_servers = cfg.bootstrap_servers
        self.client_id = cfg.client_id
        self.topics = cfg.topics

    def __new__(cls, *args):
        bootstrap_servers = args[0]['bootstrap_servers']
        client_id = args[0]['client_id']
        topics = args[0]['topics']
        if not hasattr(cls, '_users'):
            cls._users = list()
            orig = super(Single, cls)
            ob = orig.__new__(cls)
            cls._users.append(ob)
        elif not reduce(lambda x, y: x or y, map(lambda x: x.bootstrap_servers == bootstrap_servers, cls._users), False):
            orig = super(Single, cls)
            ob = orig.__new__(cls)
            cls._users.append(ob)
        elif not reduce(lambda x1, y1: x1 or y1, map(lambda x1: x1.client_id == client_id, cls._users), False):
            orig = super(Single, cls)
            ob = orig.__new__(cls)
            cls._users.append(ob)
        elif not reduce(lambda x2, y2: x2 or y2,
                        map(lambda x2: len(list(set(topics).difference(set(x2.topics)))) == 0, cls._users), False):
            orig = super(Single, cls)
            ob = orig.__new__(cls)
            cls._users.append(ob)
        else:
            for u in cls._users:
                if u.bootstrap_servers == bootstrap_servers:
                    ob = u
        return ob