The ``os`` functions generally accept any buffer-supporting object as file names, and interpret it as if ``bytes()`` had been called on it.  However, ``os.listdir(x)`` uses the type of ``x`` to know if it should return a list of bytes or a list of unicodes---and the condition seems to be ``isinstance(x, bytes)``.  So we get this kind of inconsistent behaviour:

>>> os.listdir(b".")
[b'python', b'Include', b'python-config.py', ...]

>>> os.listdir(bytearray(b"."))
['python', 'Include', 'python-config.py', ...]