Assuming there is a directory called 2008, under which is many subdirectories called 01 02…12. we want to read the files under all of the subdirectories.
there are two methods
1.

 import os
 dir='/clark/2008/'
 sub_list=[os.path.join(dir, sub) for sub in os.listdir(dir)]

2.

import glob
dir='/clark/2008/'
 

sub_list=glob.glob(dir+'*/')

More

Method 2 is simpler, and if you want to read all images under all subdirectories 01 02…12.

import glob
dir='/clark/2008/'
jpg_list=glob.glob(dir+'*/*g')