In Windows 7, FindFirstFileA uses a per-thread static buffer to decode the input bytes path to Unicode. This buffer limits the length to 259 characters (MAX_PATH - 1), even if a "\\?\" device path is used. Windows 8+ uses a dynamic buffer, but I don't see the point of switching to a  dynamic buffer on our side given Windows 7 is still so widely used and the documentation still requires Unicode for long "\\?\" paths. 

Ideally, I think 2.7 should raise the same exception as 3.5 does in this case [1]. For example:

    >>> os.listdir(long_bytes_path)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ValueError: listdir: path too long for Windows

[1]: https://github.com/python/cpython/blob/v3.5.7/Modules/posixmodule.c#L928