I've seen a few widget libs out there, but most have died quite quickly.
Here's a list of some I've found.
Sorry that it's not an answer to your question, but I think its important
to see what's out there.
Inside the Pyglet contrib module
hasn't been updated since 2007
Development has stopped
Themes are a pain in the ass and the default look is pretty horrid.
The code is nice though so could probably be forked quite easily.
Hasn't been updated since 2009
although the developer is still active here
Seems to have its own (its based on pyglet)
Not sure how complete it is.
Used by FIFE (recreating the fallout engine)
But it's bound to PyGame (SDL+PyOpenGL).
Would be interesting to see if it could be decoupled.
Unfortunately it's XML infested
Became Kivy, so I guess it's not actively developed.
I dislike Kivy, but that's a personal opinion.
These are all projects that try and invent their own UI system.
This is fine for small projects, but larger projects should aim for a more
robust UI tool such as using existing HTML / CSS renderers.
Free binding to Chromium, unlike non-free awesomium
Would be a good choice for creation of some bindings.
Kivy has bindings here:
Haven't taken a look, be good if the 'Kivy'ness could be stripped out.
Uses HTML / CSS for rendering UIs.
Unfortunately it is for C++ projects, it's 'python bindings' are actually
just for writing scripting logic inside the UI, but it doesn't let you use
it from a python project.
Took me a long time to figure that out.