Hi,
It seems your application is missing an event paint handler:
EVT_PAINT(self, self.OnPaint)
I suggest a look at:
http://wiki.wxpython.org/index.cgi/YetAnotherDrawingSample
and
http://wiki.wxpython.org/index.cgi/VerySimpleDrawing
Note: when drawing on a "wxScrollWindow", prepareDC() is important
see wxWindows Reference.
Jean-Michel Fauth, Switzerland