Re: EPICS7 and Python

["Cobb, Tom \(DLSLtd,RAL,LSCI\) via Tech-talk" <tech-talk at aps.anl.gov>]

Hi Juan,

Did you install p4p using pip, or as an EPICS module from source?

If you installed via pip, what version of epicscorelibs did it pull in?

Personally, I always install it with pip, and it pulls in a version of epicscorelibs with a matching version of epics base bundled in it. I'm not sure what happens if you try to then load a different version of epics base into the same Python process, I imagine you might get odd issues like you have seen.

My suggestion would be to make pyepics use the bundled version of epics base as suggested here:

https://github.com/mdavidsaver/epicscorelibs#using-with-pyepics-andor-cothread

Thanks,

Tom

---

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Juan F. Esteban Müller via Tech-talk <tech-talk at aps.anl.gov>
Sent: 18 August 2020 13:39
To: Cobb, Tom (DLSLtd,RAL,LSCI) via Tech-talk <tech-talk at aps.anl.gov>
Subject: Re: EPICS7 and Python

 

Hi again,

 

It seems that if I create a CA context before importing the p4p client, it all works fine. It is still a mystery for me, but it seems to be a good workaround for the moment.

 

import epics

epics.ca.create_context()

import p4p.client.thread

 

Cheers,

Juan

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of "Juan F. Esteban Müller via Tech-talk" <tech-talk at aps.anl.gov>
Reply-To: "Juan F. Esteban Müller" <JuanF.EstebanMuller at ess.eu>
Date: Tuesday, 18 August 2020 at 11:18
To: "Cobb, Tom (DLSLtd,RAL,LSCI) via Tech-talk" <tech-talk at aps.anl.gov>
Subject: EPICS7 and Python

 

Hi all,

 

I have been using CA and PVA clients in Python for some time, but in the last few days I started to have issues. I recently updated to macos Catalina and python 3.7.7, and I am using epics base 7.0.4.

 

I wrote a small script to reproduce my issues:

import time

from __future__ import print_function

import epics

import p4p.client.thread

 

pv = epics.PV('SOME:PV', connection_callback=lambda pvname,conn,pv: print('connected'))

time.sleep(1)

pv.connect(timeout=0)

pv.get()

 

This script fails to connect to the PV if I run it on python 3.7.7, using pyepics 3.4.2 with PYEPICS_LIBCA pointing to epics base 7.0.4, and p4p 3.5.1. Even trying to stop the python interpreter with ctrl-C doesn’t work, I have to kill the process. Removing the p4p import fixes the issue.

I tried different EPICS7 releases and all fail, while EPICSv3 seems to work just fine. Unsetting PYEPICS_LIBCA also works, because the internal ca lib is 3.16.

It also runs fine on python 2.7, with and without PYEPICS_LIBCA pointing to epics base 7.

 

Any clue where the issue might be? Thanks!

 

Best regards,

Juan

 

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