running python 2 vs 3

Mark Lawrence breamoreboy at
Thu Mar 20 19:56:25 CET 2014

On 20/03/2014 15:21, Marko Rauhamaa wrote:
> notbob <notbob at>:
>> I've installed python 3.3 on my Slack box, which by default comes with
>> python 2.7. I know how to fire up the different IDLE environments, but
>> how do I differentiate between the scripts? IOW, up till now, I've
>> used .py on all my 2.7 files. How do I know not to run a .py in
>> python3 or visa versa? Or do I? What's the excepted convention for
>> differentiating between the two?
> That's a bit of a sore spot.
> On a linux box, the initial line of the script indicates the
> interpreter:
>     #!/usr/bin/env python2
> for Python 2.x
>     #!/usr/bin/env python3
> for Python 3.x.
> All tutorials will tell you to start it with
>     #!/usr/bin/env python
> which will start python2 on all (?) existing linux distros, but is
> expected to start python3 within the next decade.
> Marko

The above is also true on windows via the 'Python launcher for windows' 

My fellow Pythonistas, ask not what our language can do for you, ask 
what you can do for our language.

Mark Lawrence

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