PyObjectPlus base class of most other types in the Game Engine.
Test if the object has been freed by the game engine and is no longer valid.
Normally this is not a problem but when storing game engine data in the GameLogic module, KX_Scenes or other KX_GameObjects its possible to hold a reference to invalid data. Calling an attribute or method on an invalid object will raise a SystemError.
The invalid attribute allows testing for this case without exception handling.