Even though the Tcl/Tk-based UI module called tkinter is a fairly standard part of the Python distribution and has been for ages, it often gets ignored by developers who have come to Python from other directions.
My own background is mostly in the C/C++ world, where I had deep experience with Qt and wxWidgets. That made it natural and easy to focus on wxPython when I started using Python ten years ago. I knew tkinter existed, but didn't pay it much attention.
I thought Tcl/Tk was old, odd, and obscure, which turns out not to be the best technical judgment I've ever made.