What to reference in the shebang python26 or python2.6

Question

For a Python script I need a specific Python version. Now my installation of Python 2.6 contains both python26 and python2.6

Which one should I put in the shebang?

Option 1:

#!/usr/bin/env python2.6

Option 2:

#!/usr/bin/env python26

EDIT: Yes, there is a reason not to use plain python. In some of our environments in the university python is linked to python2.4 and my code uses quite some 2.6 features.

Answer 1

Just checked on my Linux system there is only python2.6 not python26 so the former looks better.

Just to clarify, I would use conditional imports instead, in my case I need OrderedDict which is python 2.7+ only;

try:
    from collections import OrderedDict
except ImportError:
    print("Python 2.7+ is needed for this script.")
    sys.exit(1)

Answer 2

You can't always guarantee that the shebang will be used (or even that the user will have that version).

You shouldn't really limit to a specific version exactly. It's best to require at least a given version (if your code works on Python 2.6, why wouldn't it work on Python 2.7? I might not have Python 2.6 installed in a few months time.)

I would stick with the /usr/bin/env python shebang and instead dynamically detect the version. Believe it or not, the "normal" way of doing this is:

import sys
ver = sys.version[:3]

That will give you a 3-character string such as "2.6" or "2.7". I would just check that the first character = '2' (assuming you want to prevent Python 3 from running your scripts, since it's largely incompatible) and the third character >= '6'.

Edit: See Petr's comment -- use sys.version_info[0:2] instead (gives you a pair like (2, 6) or (2, 7).

Answer 3

Why don't you just use /usr/bin/python instead? Is there any reason for not doing that?

If you don't have it already, you can create a link to it using this command:

ln -s /usr/bin/python26 /usr/bin/python

This ensures compatibility if you ever upgrade your python in the future.