python function not working ?

@devernay @fabiof17
Folks is it right that Natron Python structure is like this?

GUI
	-> Effect
		-> Param
			-> Callback

If so, then I think the doc structure can be like this or at least mention as a diagram in introduction.
Please feel free to correct inherited and same classes like “AppSetting” can go in Effect stage as well.
It will clarify many problems. I can make a narrative for review as well.
Thanks.