Unable add_axis in FigureCanvasWx

I'm using matplotlib 0.54.2 (failed in 0.53.1 also) on

    > Mac OS X with Python 2.3 and wxPython, and get
    > the following traceback from this code. Looking at the
    > backend_wx.py, I can find no other mention of
    > "FigureBase" anywhere else. What should this line
    > actually be? (I tried a few thoughts, but none worked)

    > I'm basically trying to create a class that encapsulates
    > a multi-value temperature bar graph, using the Observer
    > pattern, and have inherited from the FigureCanvasWx
    > class. If this is incorrect, I'm all ears to alternative
    > suggestions.

Try replacing line 888 in backend_wx with

        FigureCanvasBase.add_axis(self, a)

Sorry for the trouble....