> try:
>   ....
> except os.error, err:
>   if WindowsError is not None or not isinstance(err, WindowsError):
>     raise   # Pretend we didn't catch it
>   pass   # Ignore it

All the double negations are hurting when I try to understand above
conditions. How about (in addition to the WindowsError name check):

if WindowsError and isinstance(err, WindowsError):
    pass # ignore

raise