Is os.path.join necessary?

Question

Currently I use os.path.join almost always in my django project for cross OS support; the only places where I don't currently use it are for template names and for URLs. So in situations where I want the path '/path/to/some/file.ext' I use os.path.join('path', 'to', 'some', 'file.ext').

However I just tested my project on windows to see whether that worked fine / was necessary and it seems windows will happily accept '/' or '\\' (or '\' when working outside of python), and as all UNIX systems all use '/' it seems like there is no reason to ever use '\\', in which case is it necessary to use os.path.join anywhere?

Is there a situation in which adding a '/' or using posixpath will cause problems on certain operating systems (not including XP or below as they are no longer officially supported)? If not I think I will just use posixpath or adding a '/' for joining variables with other variables or variables with strings and not separate out string paths (so leave it as '/path/to/some/file.ext') unless there is another reason for me to not do that other than it breaking things.

To avoid this being potentially closed as primarily-opinion based I would like to clarify that my specific question is whether not using os.path.join will ever cause a python program to not work as intended on a supported operating system.

Answer 1

The Microsoft Windows API doesn't care whether you use / or \, so it's normally fine to use either as a separator on Windows. However, command line ("DOS box" - command.com or cmd.exe) commands generally require \ in paths (/ is used to flag command options in these native Windows shells). So, for example, if you build a command line in Python and fire off a shell to execute the command, you'll generally need to use the \ separator on Windows.

One other case is covered in Lib/macpath.py: there sep is set to : (a colon), catering to older Macintosh systems. I believe that's the only system Python has ever run on that doesn't accept / as a separator.

EDIT: see here for a long account of Windows naming rules. Don't blame me ;-)

Answer 2

If you are presenting a filename to a user for any reason, it's better if that filename follows the usual OS conventions.

Windows has been able to use the / for path separators for as long as there have been paths - this was a DOS feature.