Python 单例模式

class Single(object):

    _instance = None

    def __new__(cls, *args, **kwargs):
        print('__new__')
        if cls._instance is None:
            print('create')
            cls._instance = super().__new__(cls, *args, **kwargs)
            return cls._instance

    def __init__(self):
        print('__init__')


test1 = Single()
# __new__
# create
# __init__

test2 = Single()
# __new__

保证一个类只有一个实例