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> you can't mix CRT methods with OS methods because the CRT does its 
> own buffering
Python 3's io uses the CRT's low I/O (ioinfo struct) in binary mode. It appears that the buffers pipech, pipech2, and dbcsbuffer are only used in text mode. So it should be generally OK to call get_osfhandle and use Win32 directly, if that's ever required. 
Of course, as this patch demonstrates, an io opener (3.3+) can call open_osfhandle immediately after CreateFile, and nothing else changes. This could be added to io / _pyio in 3.5. Initially it could simply be a pure-Python function that uses _winapi and msvcrt. 3.6 could get a C implementation in _iomodule.c.