Basically a reopen of the older issue8485 with the same name. It was decided there to drop support for bytearray filenames -- partly because of the complexity of handling buffers but it was also deemed to just not make much sense.

This regressed or crept back into the posix module with the big path_converter changes for 3.3:

https://hg.python.org/cpython/file/ee9921b29fd8/Lib/test/test_posix.py#l411

IMHO this functionality should be deprecated/removed per the original discussion, or does someone want to reopen the debate?

The os module docs (and path_converter's own docs) explicitly advertise handling of str or bytes, not bytearrays or buffers. Even os.fsencode rejects bytearrays/buffers.

Related to issue26754 -- further inconsistencies around filename handling