Difference between class parameter and instance parameter:
1. instance parameter is static storage, it's only initialized once no matter how many times invoking, and memory address not change during the whole progress ; It will not be released untill the program exits. It works in the area of instances.
2. class parameter is automatic storage, it's released as soon as after called, and will be initialized not only once; it works only in the class area before instance invoked, such as __init__ instance.
In example codes below, the class parameter 'no_inst' is initialized every time only if the class is invoked, and value is always set to be 0; but, the instance parameter 'Kls.no_inst' remains in the memory, it is initialized only once, and the value adds by 1 in every invoking.
