IndexError：列表索引超出范围？

Question

当我运行以下程序时

def generate_list(frame_path):
    result = open('./labels/ucf_labels.txt','w')
    for root_dir, dirs, files in os.walk(frame_path):
        print('root_dir:', root_dir)  # current dir
        print('sub_dirs:', dirs)  # all subdirectories under the current path
        print('files:', files)  # all non_directory sub_files in the current path
        r = r'clip(.*)_'
        re_frame = re.compile(r)
        for frame_name in files:
            frame_path = root_dir+'/'+frame_name
            label = re.findall(re_frame,root_dir)[0] #frame2label mapping
            result.write(frame_path+' '+str(label)+'\n')

我遇到以下错误：

Traceback (most recent call last):
  File "/home/tl/frame_extract.py", line 51, in <module>
    generate_list('./segments')
  File "/home/tl/frame_extract.py", line 46, in generate_list
    label = re.findall(re_frame,root_dir)[0] #frame2label mapping
IndexError: list index out of range

标签的索引似乎超出范围，但是我找不到解决方案。有人帮忙吗？