How do I tell a Python script to use a particular version

Question

How do I, in the main.py module (presumably), tell Python which interpreter to use? What I mean is: if I want a particular script to use version 3 of Python to interpret the entire program, how do I do that?

Bonus: How would this affect a virtualenv? Am I right in thinking that if I create a virtualenv for my program and then tell it to use a different version of Python, then I may encounter some conflicts?

Answer 1

You can add a shebang line the to the top of the script:

#!/usr/bin/env python2.7 

But that will only work when executing as ./my_program.py.

If you execute as python my_program.py, then the whatever Python version that which python returns will be used.

In re: to virtualenv use: virtualenv -p /usr/bin/python3.2 or whatever to set it up to use that Python executable.

Answer 2

Perhaps not exactly what you asked, but I find this to be useful to put at the start of my programs:

import sys  if sys.version_info[0] < 3:     raise Exception("Python 3 or a more recent version is required.")