Return the absolute path to the installed OpenType font having
        *family_name* and the styles *is_bold* and *is_italic*.

def find(cls, family_name, is_bold, is_italic):
        """
        Return the absolute path to the installed OpenType font having
        *family_name* and the styles *is_bold* and *is_italic*.
        """
        if cls._font_files is None:
            cls._font_files = cls._installed_fonts()
        return cls._font_files[(family_name, is_bold, is_italic)]