Proper shebang for python3

[Chris Angelico]

On Sun, Jul 21, 2019 at 9:15 AM Cameron Simpson <cs at cskk.id.au> wrote:
>
> On 21Jul2019 08:14, Chris Angelico <rosuav at gmail.com> wrote:
> >On Sun, Jul 21, 2019 at 5:26 AM Tim Daneliuk <info at tundraware.com> wrote:
> >> So, no, do NOT encode the hard location - ever.  Always use env to discover the one that
> >> the user has specified.  The only exception is /bin/sh which - for a variety of reasons -
> >> can reliably counted upon.
> >
> >A quick grep through my $PATH shows that there are a number of
> >executable Python scripts there, including add-apt-repository,
> >calibre, some lilypond stuff, trash-can management, samba-tool, iotop,
> >and youtube-dl. If I have a venv active with, say, Python 3.9, then
> >`/usr/bin/env python` is going to point to Python 3.9. What are the
> >odds that all those scripts will work with Python 3.9 with no
> >libraries installed? Why should typing "youtube-dl B7xai5u_tnk" be
> >affected by a virtual environment, when typing "man youtube-dl"
> >wouldn't be?? Using env for everything is a terrible idea and one that
> >will basically make virtual environments useless.
>
> I'm with Tim Daneliuk. The environment matters and should be honoured
> except in extremely weird cases.
>
> If you require a specific outcoming, set a specific environment. It is
> under your control. Control it.
>
> For your specific example, "man youtube-dl" _is_ affected by the
> environment. It honours the $MANPATH variable.
>
> For Peter J. Holzer, if we must play the "I've been doing this forever"
> game: I've been sysadmining etc longer than your 25 years and disagree
> with you. If your tools are strongly affected by version, run them with
> an environment that finds the right version.
>
> Installers, particularly those run as root or in other low level setup
> situations, should have a WELL DEFINED environment.
>
> If you have a tool that isn't portable, put it in a wrapper that coddles
> its behaviour.

So.... you mean that a tool that depends on running on a consistent
environment, it should use a shebang of "/usr/bin/python3.6" instead
of "/usr/bin/env python3"? Because, wow, that would be exactly what is
already happening on my system. Why use /usr/bin/env and then wrap
something around it to force the environment, when you could just set
a correct shebang so it properly defines its execution environment?

ChrisA