They are same, but which one should I use?
http://docs.python.org/library/os.html:
os.sep The character used by t
os.sep
The character used by t
If you are using Jython 2.7, I suggest using os.sep (works) instead of os.path.sep (broken) as Jython on Windows has a bug returning a "/" slash instead of the required "\" backslash.
os.path.sep
"/"
"\"