The trend these days is to just use Electron. It seems like more and more apps (Slack, WordPress, Ghost, Postman, Visual Studio Code, etc.) are drinking the cross platform cool aid. I read this article which discusses some of the negative aspects of choosing Electron as a GUI framework. Drew makes some great points and the following paragraph inspired me to once again take a stab at actually learning a proper GUI framework.
PyGObject (aka PyGI) is the new way of developing GTK+ 3 GUI applications in python. On Ubuntu, installing the python3-gi package is enough to get started making your application “do something”. I found an excellent tutorial on using PyGI which does a great job explaining both basic and advanced concepts.
This tutorial gives an introduction to writing GTK+ 3 applications in Python.
In addition, this tutorial also has a section on how to use Glade, which is a GUI tool for building GUIs. For any substantial project hard coding the UI is going to get old pretty quickly.
The Python GObject Introspection API is massive. It solves a lot of common problems and also lets you work with a lot of existing GNOME applications. Looking forward to making something useful soon.