instances = {}

def singleton(cls):
    def get_instance(*args, **kw):
        cls_name = cls.__name__
        print('===== 1 ====')
        if not cls_name in instances:
            print('===== 2 ====')
            instance = cls(*args, **kw)
            instances[cls_name] = instance
        return instances[cls_name]
    return get_instance

@singleton
class User:
    _instance = None

    def __init__(self, name):
        print('===== 3 ====')
        self.name = name

u1 = User("guan")
u2 = User("guan")
print (u1 is u2)