Whatever it is you're trying to do, I'm sure there is a better way. A decorator is not really made to track state between different calls, especially calls to different object instances. It's hard to say exactly why it breaks because
a. You don't give the complete error. What line? what context?
b. The code above is not runnable and only shows isolated parts.
If you can post a runnable example, that would help. But please also state what you are trying to do. I'm sure there is an easier, more readable way to do it.
Cheers