Return a dict mapping a font descriptor to its font file path,
        containing all the font files resident on the current machine. The
        font descriptor is a (family_name, is_bold, is_italic) 3-tuple.

def _installed_fonts(cls):
        """
        Return a dict mapping a font descriptor to its font file path,
        containing all the font files resident on the current machine. The
        font descriptor is a (family_name, is_bold, is_italic) 3-tuple.
        """
        fonts = {}
        for d in cls._font_directories():
            for key, path in cls._iter_font_files_in(d):
                fonts[key] = path
        return fonts