def _rename_existing_file(filename):
    if os.path.isfile(filename):
        suffix = filename.split('.')[-1]
        new_filename = filename.replace('.{}'.format(suffix),
                                        '_{}.{}'.format(_get_now_timestamp(), suffix))
        os.rename(filename, new_filename)
        _progress_warning('renamed existing {} file {} -> {}'.format(suffix, filename,
                                                                     new_filename))