Error trying to extend MessageBox

Why can't MessageBox be extended, while Frame can?
I'm new, are there other widgets known to have this issue?

Python 2.5.2 (r252:60911, Feb 22 2008, 07:57:53)
[GCC 4.0.1 (Apple Computer, Inc. build 5363)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import wx
>>> class C(wx.MessageBox):
... pass
...
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
TypeError: Error when calling the metaclass bases
     function() argument 1 must be code, not str
>>> class F(wx.Frame):
... pass
...
>>>

This is using wx-2.8-mac-ansi.

Thanks for reading this. Please reply directly if possible.

Scott