My favorite is the python-based Urwid library at http://www.urwid.org. It was a little hard for me to wrap my head around it at first, but once you get it, you can write TUI applications without a lot of code. Easy to install, many examples to work from.
How popular is it in the Python space? I loved the large text widget and would love to contribute with a font using the Teletext 2x3 mosaics that got into Unicode 13 (which are fully supported in VTE)
Also check out the list of applications built with Urwid [2]. Probably the two most popular applications that use Urwid are bpython [3] (an alternative Python REPL that is really nice), and PUDB [4] (a nice Python debugger that is reminiscent of Borland's Turbo Pascal). I use bpython all the time, it's a lifesaver, and I occasionally fire up PUDB when I am really stuck on something.
I've used Urwid in a couple of projects (most notably Zeitzono [5]), it's nice in that it's fairly high level and gives you a number of helpful widgets to work with. Starting with it from scratch is a little daunting, so you should look at existing projects to see how they are using the library. Also, I believe Urwid development has slowed down somewhat in the last few years (although other folks maybe stepping up to take over from the original author, I haven't follow up on this in a while).
Also definitely take a look at Python Prompt Toolkit [6]. They started off as library for writing line-oriented command interpreters, but now can also be used for building full screen applications. I've not yet built an application using it, but it looks really good and is actively developed. ptpython [7] is a REPL built using this library and gives bpython a run for its money.
[1] https://pypistats.org/packages/urwid
[2] https://github.com/urwid/urwid/wiki/Application-list
[3] https://bpython-interpreter.org/
[4] https://github.com/inducer/pudb