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Date:   Wed, 4 Mar 2020 06:42:14 +0100
From:   Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
To:     "Bird, Tim" <Tim.Bird@sony.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        "tbird20d@gmail.com" <tbird20d@gmail.com>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] scripts/sphinx-pre-install: add '-p python3' to
 virtualenv
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Em Tue, 3 Mar 2020 17:07:48 +0000
"Bird, Tim" <Tim.Bird@sony.com> escreveu:

> > -----Original Message-----
> > From: Jonathan Corbet <corbet@lwn.net>
> > 
> > On Mon, 24 Feb 2020 18:34:41 -0700
> > tbird20d@gmail.com wrote:
> >   
> > > With Ubuntu 16.04 (and presumably Debian distros of the same age),
> > > the instructions for setting up a python virtual environment should
> > > do so with the python 3 interpreter.  On these older distros, the
> > > default python (and virtualenv command) might be python2 based.
> > >
> > > Some of the packages that sphinx relies on are now only available
> > > for python3.  If you don't specify the python3 interpreter for
> > > the virtualenv, you get errors when doing the pip installs for
> > > various packages
> > >
> > > Fix this by adding '-p python3' to the virtualenv recommendation
> > > line.
> > >
> > > Signed-off-by: Tim Bird <tim.bird@sony.com>  
> > 
> > I've applied this, even though it feels a bit fragile to me.  But Python
> > stuff can be a bit that way, sometimes, I guess.  
> 
> I agree it seems a bit wonky.

Well, we could, instead, add some code that would be checking python and pip
versions, but still distros could be doing some backports with could
cause side-effects. So, checking for distro versions as done in this patch
seems a lot safer.

> The less fragile approach would have been to just
> always add the '-p python3' option to the virtualenv setup hint,
> but Mauro seemed to want something more fine-tuned.

Yeah, I asked for a more fine-tuned version.

Depending on python/pip version, adding a -p python3 seems to cause
troubles (at least I found some bug reports about that). I may be
wrong (it was a long time ago), but, before adding the logic that checks
for "python3" I guess I tried first add -p python3, but, back then,
I found some troubles (probably with some old Fedora version).

So, better to use this syntax only on distros we know it will
work as expected.

> As far as the string parsing goes, I think that the format of strings
> returned by lsb-release (and the predecesors that sphinx_pre_install
> checks) is unlikely to change.

Since when we added this script, we didn't have any troubles yet with
the part of the code with checks the distribution version. So, I guess
that the lsb-release related checks are pretty much reliable.

> 
> Thanks for applying it.
>  -- Tim
> 
>