def METHOD_NAME(directory_name, since=None):
    check.str_param(directory_name, "directory_name")
    if not os.path.isdir(directory_name):
        return []
    try:
        since = float(since)
    except (TypeError, ValueError):
        since = None
    files = []
    for filename in os.listdir(directory_name):
        filepath = os.path.join(directory_name, filename)
        if not os.path.isfile(filepath):
            continue
        fstats = os.stat(filepath)
        if not since or fstats.st_mtime > since:
            files.append((filename, fstats.st_mtime))
    return files