Unable to run winpdb

Question

I tried to run winpdb.py, but I got an error saying that it could not find wxPython. This is strange to me because I know I have wxPython installed and included in my PYTHONPATH. I can import wx in the Python interpreter.

Mac OS X 10.5.8
Python 2.6
PYTHONPATH=/sw/lib/python2.6/site-packages/:/usr/local/lib/wxPython-unicode-2.8.10.1/lib/python2.6/site-packages/wx-2.8-mac-unicode:

$ python winpdb.py  
wxPython was not found.  
wxPython 2.6 or higher is required to run the winpdb GUI.  
wxPython is the graphical user interface toolkit used by Winpdb.  
You can find more information on wxPython at http://www.wxpython.org/  
The Unicode version of wxPython is recommended for Winpdb.  
To use the debugger without a GUI, run rpdb2.  

What could be causing this?