Hmm, yes, I see that the open() builtin doesn't accept bytes
filenames, though os.open() still does.  When I saw that you
could pass bytes filenames transparently from os.listdir() to
os.open(), I assumed that this was intentional!

So what *is* os.listdir() supposed to do when it finds an
unconvertible filename?  Raise an exception?  Pretend the file
isn't there?  What if someone puts unconvertible strings in the
password database?  I think this is going to cause real problems
for people.