Return the archive path for file with real_path.

        Mapping is based on removal of self.path_prefix which is determined
        by self.check_files().

def archive_path(self, real_path):
        """Return the archive path for file with real_path.

        Mapping is based on removal of self.path_prefix which is determined
        by self.check_files().
        """
        if (not self.path_prefix):
            return(real_path)
        else:
            return(os.path.relpath(real_path, self.path_prefix))