Return a sequence of directory paths likely to contain fonts on the
        current platform.

def _font_directories(cls):
        """
        Return a sequence of directory paths likely to contain fonts on the
        current platform.
        """
        if sys.platform.startswith('darwin'):
            return cls._os_x_font_directories()
        if sys.platform.startswith('win32'):
            return cls._windows_font_directories()
        raise OSError('unsupported operating system')