Both wxPython and the wxWidgets library it is built upon are mature projects that are still actively developed. wxPython's history started before the turn of the century, back in 1996. wxWidgets was already around 4 years old by then, you can see more details about the history of wxWidgets here.
History according to Robin
In 1995 I was working on a project that needed a GUI to be deployed on HP-UX systems, but my boss also wanted to show something at a trade show on his Windows 3.1 laptop in a few weeks time. So I started searching for a cross platform C++ GUI toolkit to do a prototype with. In those days it wasn't so easy without Google, but I found that there were several commercial alternatives available (none of which are still available today) and lots of toolkits with freely available source.
While evaluating each of the free toolkits for my immediate needs and deciding which of the commercial offerings would be best for our long term needs I ran into the term "Python bindings" on the wxWidgets web site (in this case "binding" refers to the connection between the Python language and the wxWidgets toolkit). Full of curiosity at how one would "bind" a software toolkit to a reptile (I had never heard of the Python language up to this point), I clicked on the link, and the next link, and the next, until I finally ended up at the Python 1.2 Tutorial document. Three hours later I was converted from being the local C++ Guru to a Python Evangelist bugging all the developers in the immediate vicinity showing them the cool new thing I had discovered.
So instead of working on my prototype I worked with Harri Pasanen in Finland to advance the Python bindings for wxWidgets, otherwise known as wxPython 0.2, also with some help from Edward Zimmerman. We got it to be functional enough that I could do my prototype for my boss using Python, but wxPython was a nightmare to maintain and to enhance because everything (C++ extension module code, Python proxy modules, build system, etc.) was all done by hand, and little changes or enhancements to wxWidgets would often require changes to several places in wxPython code to add the support for the enhancement or fix to wxPython. When it reached many tens of thousands of lines of code it got to be very awkward and fragile to work on in that manner. Add to that the fact that there was no central source code repository (this was also long before SourceForge's time) and so we were emailing code changes to each other and you can get an inkling for the difficulties involved.
About that time I had to start doing real work again as my main project at work started to build up from a gleam in the eye to a full force development project with several developers under my control and design meetings and deadlines and all that, and I found myself fully back in the C++ world again, (although I was able to use Python for some of the build and test scripts for the project.) Harri also wasn't able to spend any time on it, and so wxPython development slowed to less than a crawl and eventually pretty much stopped.
In 1997 I discovered SWIG (the Simple Wrapper and Interface Generator,) and realized that it could help with all the maintenance issues that pained us in the wxPython project. In about three or four weeks worth of spare time I almost completely reimplemented using SWIG everything (and more!) that had taken several weeks of almost full time on my part and several months of part time for Harri doing it by hand. After getting sidetracked on another project for a while I discovered that wxWidgets 2.0 was in active development, but had a whole new architecture, so I had to do it all again. But this time the new architecture simplified things enough that it took only about a weeks worth of spare time! So in the summer of 1998 the first "modern version" of wxPython was released and has been in active development ever since. The first announcement is archived here.
The rest is, as they say, history. It's important to note however that SWIG is allowing me to easily create and maintain literally hundreds of thousands of lines of code, so much of the credit for the vastness of wxPython's feature set deserves to go to David Beazley and the other developers contributing to that project.
History of Project Phoenix
The "recent" changes page of wxPython goes all the way back to release 0.3 in 1998. That was a long time ago, with many releases made since then. The changelog is updated for each release and is viewable here.