> Though I don't have any idea if it works on Windows, but it seems 
> properly factored.

Generally it should. However, os.get_terminal_size is unnecessarily limited to the standard handles with a hard-coded mapping 0 => StandardInput, 1 => StandardOutput, and 2 => StandardError, and otherwise raises ValueError. Example failure:

    >>> fd = os.open('conout$', os.O_RDWR)
    >>> os.isatty(fd)
    True
    >>> os.get_terminal_size(fd)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ValueError: bad file descriptor

There is no need to involve the standard handles. It should call _get_osfhandle(fd).