The file tree contains a file which has an undecodable character in it. It ends up mangled as specified in PEP 383.
Priting such filenames is not directly supported (since they have invalid characters in them), but you can workaround it in several ways, for example escaping all non-ASCII chars: `print(ascii(f))`.

(note that opening the file will still work fine; only outputting the filename without special care will fail)

Python 2 is different since it doesn't attempt to decode filenames at all, it just treats them as opaque bytes.