Unix paths that work for any platform in Python?

Question

Can all paths in a Python program use ".." (for the parent directory) and / (for separating path components), and still work whatever the platform?

On one hand, I have never seen such a claim in the documentation (I may have missed it), and the os and os.path modules do provide facilities for handling paths in a platform agnostic way (os.pardir, os.path.join,…), which lets me think that they are here for a reason.

On the other hand, you can read on StackOverflow that "../path/to/file" works on all platforms…

So, should os.pardir, os.path.join and friends always be used, for portability purposes, or are Unix path names always safe (up to possible character encoding issues)? or maybe "almost always" safe (i.e. working under Windows, OS X, and Linux)?

Answer 1

I've never had any problems with using .., although it might be a good idea to convert it to an absolute path using os.path.abspath. Secondly, I would recommend always using os.path.join whereever possible. There are a lot of corner cases (aside from portability issues) in joining paths, and it's good not to have to worry about them. For instance:

>>> '/foo/bar/' + 'qux'
'/foo/bar/qux'
>>> '/foo/bar' + 'qux'
'/foo/barqux'
>>> from os.path import join
>>> join('/foo/bar/', 'qux')
'/foo/bar/qux'
>>> join('/foo/bar', 'qux')
'/foo/bar/qux'

You may run into problems with using .. if you're on some obscure platforms, but I can't name any (Windows, *nix, and OS X all support that notation).