Yes, it is not that easy. I was able to create some Nim examples, see GTK4 for Graphical User Interfaces
My guess is that it should work very similar for Python. Generally, what works in Nim, does work of course in C, and should work with Python. Unfortunately not the other way round, the gintro Nim bindings are a bit restricted still 
I spent a lot of time on these examples, I guess some weeks fulltime.
[EDIT] For Python, during my research I found this one: Reorder rows in a list (GTK4) - #4 by SoongNoonien