Switching this to a docs bugs, since http://docs.python.org/3/library/functions.html#open doesn't mention this behaviour at all, and http://docs.python.org/3/library/io.html#io.FileIO.name only notes the fact it may be a file descriptor without mentioning the str/bytes discrepancy.

So, at a bare minimum, we need to clearly describe this behaviour in the docs. We may also want to explicitly point out that using os.fsdecode(name) before passing it to open() will ensure that the name attribute is set to a string rather than a bytes object.