def METHOD_NAME(extensions):
    files = []
    if len(args.filenames) > 0:
        files = args.filenames
    else:
        for root, dirs, walkfiles in os.walk(args.rootdir):
            # don't visit certain dirs. This is just a performance improvement
            # as we would prune these later in normalize_files(). But doing it
            # cuts down the amount of filesystem walking we do and cuts down
            # the size of the file list
            for d in skipped_dirs:
                if d in dirs:
                    dirs.remove(d)
            for name in walkfiles:
                pathname = os.path.join(root, name)
                files.append(pathname)
    files = normalize_files(files)
    outfiles = []
    for pathname in files:
        basename = os.path.basename(pathname)
        extension = file_extension(pathname)
        if extension in extensions or basename in extensions:
            outfiles.append(pathname)
    return outfiles