[Linux-SIG] Revisit of PEP 394 -- The "python" Command on Unix-Like Systems

[Barry Warsaw]

Nick Coghlan wrote:

> = Approach 3: add a magic script comment to opt-in to trying Py3 =
>
> This whole problem just doesn't feel like a per-script setting to me -
> it feels like a system administrator setting, where they say either
> "Yes, I am confident in my ability to debug errors arising from myself
> and others trying to run Python 2 scripts on Python 3", or "I want to
> preserve compatibility with older Py2 only systems for now, even if
> that means running parallel Python stacks on my newer systems".

I think it *is* a per-script setting.  Remember that we're trying to fix 
the problem of what /usr/bin/python means to 1) third party scripts that 
the platform has no control over; 2) the CLI UX.

Now, a system administrator managing a suite of shebanged third party 
scripts for their organization should be able to change the mux'd 
default.  As much as I hate introducing a configuration file, I think 
that's going to be appropriate here.  That would allow:

* A system admin to select the system-wide default Python version, 
assuming the platform provides the option of different versions;

* Individual scripts can make their own selection, overriding the system 
defaults;

* Individual users can override the script selection by setting an 
environment variable.

* A user at the command line could also provide a switch to make the 
selection.

Cheers,
-Barry