The documentation for os.listdir should mention that there's a 
possibility that it can fail to decode paths to unicode objects and that 
it returns str objects for those paths it couldn't decode.

The documentation should also explain when this might happen, and 
perhaps how to deal with it. The cases that this could happen or how to 
work around it are beyond my knowledge, but #683592 does mention 
something about resetting the locale. I don't know if that comment is 
still relevant, or if it applies to all cases of decoding failure, 
however.

I don't know if this behavior still exists in Python 2.6. If it does, 
the documentation for 2.6 should be amended as well.