Still using tkinter here which is python's default GUI, what's the license for PyQt5? For me learning Qt in general is another big investment of limited time, so far I have been using tkinter with python and it works well.
You then need a license for QT, which is LGPL or commercial. You can use the LGPL version of Qt with commercial PyQt, but I never understood the hoops you might have to jump through in order to comply with the LGPL. Packaging python apps is painful enough without having to worry about that, might as well spend a little to avoid the aggravation. LGPL Qt also lacks a few advanced packages.
Do note that the PyQt5 authors (Riverbank Computing) have made it explicit that their view of GPL linking (a matter of debate in some circles) is that you can use PyQt5 from MIT/BSD/... applications.
