paython问题，在图片路径后面加一个\t，后面是分类id，怎么加呀

f=open('train_list.txt','w')
path = "foods"
index = 0
for dirname in os.listdir(path):
    for fname in os.listdir(path+"/"+dirname):
        f.write(path+"/"+dirname+"/"+fname+"\t"+"\n")
    index = index+1
    str(index)
f.close()