wxPython is a cross-platform GUI toolkit for the Python programming language. It allows Python programmers to create programs with a robust, highly functional graphical user interface, simply and easily. It is implemented as a set of Python extension modules that wrap the GUI components of the popular wxWidgets cross platform library, which is written in C++.

As for python 2, wxPython 3.x is depricated. Supporting wxPython 4 is a necessary step in the migration to python 3.

wxPython 4 together with wxPython 3

A dedicated branch supports wxPython 4. That branch cannot merge with default branch, since many changes are incompatibles. Both branches will be maintained until WxPython 3 can be safely dropped.