Re: [Buildroot] Python pyc only and problem with scripts

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

Hello Federico,

On Mon, 8 Aug 2022 09:40:02 +0200
Federico Pellegrin <fede@evolware.org> wrote:

> I've found a minor problem related to the rt-tests package, but that maybe
> is slightly more generic and wanted to report and in case understand which
> approach would be best to fix it (and contribute a patch then if possible).
> 
> The specific problem: rt-tests, besides a few compiled executables,
> installs also two tools which are written in Python, namely hwlatdetect and
> get_cyclictest_snapshot. These are Python scripts which get installed in
> the PYLIB and then a symbolic link is done from /usr/bin to them, so ie we
> have: /usr/bin/hwlatdetect ->
> /usr/lib/python3.10/site-packages//hwlatdetect.py
> 
> Needless to say that once the pycompile.py script is run and original .py
> files are removed, of course in the "PYC only" setup (which is the
> default), then the link is broken and it will not work.
> Additionally that pyc files will not work for scripts like that, so just
> somehow fixing the link mentioned above would anyhow not work, as you need
> to execute them eventually by explicitly naming the interpreter.
> 
> I could imagine that we could have some similar other cases when we are
> installing Python scripts directly executed in PYLIB and not modules. But
> I'm not sure that installing the scripts there is a good idea as well,
> comparing with other distros that doesn't seem to be the case.
> So maybe the problem is really in rt-tests after all and the location those
> scripts get installed and I may just fix it that way (and contact upstream)?
> Otherwise should it be more generic maybe could make sense to have a
> facility to list some files that should not be converted to PYC?

Thanks for your bug report.

My initial gut feeling would indeed be that it is strange to install
scripts in /usr/lib/python, and they should be installed in /usr/bin
instead, so that /usr/lib/python is only for Python modules that can be
byte-compiled. However, I am not an expert at all in terms of Python
best practices and latest standards.

But from a Buildroot perspective, it really makes a lot of sense to be
able to do the byte-compilation at build-time (to save on startup time)
and drop the .py files (to save on filesystem footprint).

For the rt-tests case, I would therefore suggest to move those scripts
to /usr/bin.

Of course, if that problem shows up in more packages, then yes we could
think of a mechanism for packages to declare a number of py files that
should not be byte-compiled, and that should be preserved on the target.

Best regards,

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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