Re: EPICS7 and Python

[Matt Newville via Tech-talk <tech-talk at aps.anl.gov>]

Hi Juan

On Tue, Aug 18, 2020 at 11:27 AM Juan F. Esteban Müller <JuanF.EstebanMuller at ess.eu> wrote:

Thanks for your replies, Tom, Michael, and Matt.

 

It looks like indeed the problem is that pyepics is using a different version of the EPICS libraries. I might have been confused about how this is done.

 

I installed pyepics and p4p using pip, and it was fetching epicscorelibs, but then I was setting PYEPICS_LIBCA to use a patched 7.0.4 to fix a couple of other issues I was having (https://github.com/epics-base/pva2pva/pull/34, https://github.com/epics-base/epics-base/issues/83).

It seems that pyepics is using that environment variable, but p4p is ignoring it, so each module is trying to load different versions of the libraries. I was probably lucky that it worked in the past with Python 3.7.3 on macos Mojave and on Python 2.7.

 

I believe they would need to load the same version of libca (that is, if p4p loads libca - I'm not sure it does).   But it does work to use the pyepics-default libca / libCom, which are definitely not going to be seen or used by p4p.  So, that seems a little strange.    Maybe there is something different with 7.0.4?

Anyway, that's why pyepics has the PYEPICS_LIBCA environmental variable and does not load the library at import time, but waits as late as possible to load the library.

--Matt