Well, that seems complicated: you can't overwrite a io.FileIO().name attribute, and doing so would be nonsensical for tarfile, which would try to perform IO operations on a random file descriptor... Also, I can't think of any case where a .name attribute could actually be bytes (I was just mirroring the code in msg214670).

Here's a patch that tries all combinations of encoding for writing, but I can't see a way to enforce manually the name attribute being an int, even for this test purposes.