```python def singleton(cls): instances = {} def _singleton(*args, **kwargs): if cls not in instances: instances[cls] = cls(*args, **kwargs) return instances[cls] return _singleton @singleton class MyClass3(object): a = 1 one = MyClass3() two = MyClass3() print id(one) # 29660784 print id(two) # 29660784 print one == two # True print one is two # True ```