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.



class ociTemperatureGraph(FigureCanvasWx, Observer):
     def __init__(self, parent):
         wxPanel.__init__(self, parent, -1)
         self.fig = Figure((3,3), 75)
         self.subplot = Subplot(self.fig, 111)
         self.add_axis(self.subplot) <<-- blows up here

Traceback (most recent call last):
   File "./ociTemperatureGraph.py", line 86, in ?
   File "./ociTemperatureGraph.py", line 74, in main
     frame = PlotFigure()
   File "./ociTemperatureGraph.py", line 60, in __init__
     self.fig = ociTemperatureGraph(self)
   File "./ociTemperatureGraph.py", line 42, in __init__
   File "/System/Library/Frameworks/Python.framework/Versions/2.3/lib/python2.3/site-packages/matplotlib/backends/backend_wx.py", line 888, in add_axis
     FigureBase.add_axis(self, a)
NameError: global name 'FigureBase' is not defined