Re: Python installation paths

[Richard Laager <rlaager@debian.org>]

On 6/2/22 14:15, Alec Leamas wrote:
> Hi Audrey
>
> On 02/06/2022 20:16, Andrey Rahmatullin wrote:
> > On Thu, Jun 02, 2022 at 07:19:56PM +0200, Alec Leamas wrote:
> > > Dear list,
> > >
> > > I try handle a package which installs a partly compiled,
> > > architecture-dependent python module. Until now  this has been done in
> > > /usr/lib/triplet/python3.10/site-packages. This scheme has basically 
> > > worked
> > > fine.
> > >
> > > However, here is an Ubuntu bug [1] where a user runs into problems 
> > > because
> > > this installation path is not in sys.path by default.
> > >
> > > I have been trying to look in the python policy docs, but cannot find 
> > > the
> > > exact way to install code like this, in the policy [2]
> > > parlance an "extension module".
> > Not sure where is this documented but you can easily check on your 
> > system.
> > It should be 
> > /usr/lib/python3/dist-packages/*.cpython-3*-x86_64-linux-gnu.so
>
>
> Hm...this is not what I have. Did I get get the term "Extension module" 
> wrong?

There are a couple different ways to do Python to C. I think the terms 
are CFFI (or FFI or ctypes, maybe some of those are different though?) 
vs CPython extension, but I'm not 100% certain of that.

I maintain the ntpsec package. IIRC, upstream is transitioning (but I 
think still supports both at the moment).

On an older version, I had this (from the python3-ntp binary package):

/usr/lib/python3/dist-packages/ntp
/usr/lib/python3/dist-packages/ntp/__init__.py
(other .py files omitted)
/usr/lib/python3/dist-packages/ntp/ntpc.cpython-38-x86_64-linux-gnu.so

I believe that is the extension approach. I think the way this works is 
that if you import ntpc, it imports the .so. Note that there is no ntpc.py.

On newer python3-ntp, using the FFI approach, I have this:

/usr/lib/python3/dist-packages/ntp/__init__.py
/usr/lib/python3/dist-packages/ntp/ntpc.py
(other .py files omitted)
/usr/lib/x86_64-linux-gnu/ntp/libntpc.so
/usr/lib/x86_64-linux-gnu/ntp/libntpc.so.1
/usr/lib/x86_64-linux-gnu/ntp/libntpc.so.1.1.0

In this approach, ntpc.py has explicit code to load libntpc.so from 
/usr/lib/x86_64-linux-gnu/ntp/ (that path being subst'ed in to ntpc.py 
by the build process).

I hope that helps.

--
Richard

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