directory

[Gold Fish]

How to read the subdirectories in the directory
Support i have the directory /home/ which have some subdirectories
/home/sub1
/home/sub2
/home/sub3
I am using os.listdir('/home/') to read in the list so it will be 
['sub1','sub2','sub3'] now i want to read inside the sub directory sub2
once again i using os.listdir(os.listdir('/home/')[1]) but it came out with 
an errors: not a file or directory. Can anyone tell me what did i wrong. 
Anh how to fix it.