["python","operating-system"]
which one should I use: os.sep or os.path.sep?

They are same, but which one should I use? http://docs.python.org/library/os.html: os.sep The character used by the operating system to separate pathname components. This is '/' for POSIX and '\' for Windows. Note that knowing this is not sufficient to be able to parse or concatenate pathnames — use os.path.split() and os.path.join() — but it is occasionally useful. Also available via os.path.
I'd use os.path.sep to make it very clear that it's the path separator… But consistency is more important, so if one is already being used, use that. Otherwise, pick one and use it all the time. Edit: Just to make sure you're not reinventing the wheel, though, the path module already has join, split, dirname, and basename functions… So you should rarely need to use os.sep: >>> os.path.join("foo", "bar", "baz") 'foo/bar/baz' >>> os.path.split(_) ('foo/bar', 'baz')