Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Thu, 27 Oct 2022 16:16:58 -0400

Hi Kuktae,

On 10/25/22 19:29, Kim, Kuktae via Tech-talk wrote:

Hi all,
I am trying to use the P4P python module (https://mdavidsaver.github.io/p4p/index.html# <https://mdavidsaver.github.io/p4p/index.html#>) in Matlab for EPICS NTTable PVs.

Versions that I use:
*/Python: 3.8.13/*
*/P4P: 4.1.3/*
*/Matlab: 2020a/*

Wow, so matlab can call into cpython now?
This is news to me.

First, I tested pvget and pvput in linux terminal, then moved to python and Matlab for each step. It works without problem for the NTScalar and NTScalarArray types. But I don't know how to implement for NTTable type. I will put more information below.

You have found the NTTable helper, which doesn't actually
do that much wrt. the Type definition.

https://github.com/mdavidsaver/p4p/blob/5717342c2c1ddd74217298decab7ce52faa60006/src/p4p/nt/__init__.py#L157-L164

You can also use the NTTable wrapper when setting up the
client Context.  Which may or may not be helpful in your
application.

ctxt = p4p.client.thread.Context(nt={"epics:nt/NTTable:1.0": p4p.nt.NTTable})

With this, ctx.get() will implicitly call NTTable.unwrap()

...

*/In the Python command line, work fine; but pvget doesn't show a whole table./*

...

from p4p.client.thread import Context
MatP4P = Context('pva')
MatP4P.get('TEST:TBL')

Value(id:epics:nt/NTTable:1.0, Value(['device_1', 'device_2']))     # <== P4P doesn't show whole information such as in linux terminal

To avoid excessive console output, the repr() implementation for Value does not recurse.
You might investigate Value.tolist(), .todict(), or .tostr()

https://mdavidsaver.github.io/p4p/values.html#p4p.Value.tolist

...

*/In Matlab command line, pvput shows error message. Due to the colon operator.

...

MatP4P.put('TEST:TBL', {'value.name': ['test1', 'test2'], 'value.number': [10, 20]})

Warning: Colon operands must be real scalars.

Error using  :

For colon operator with char operands, first and last operands must be char.

This looks like a matlab syntax error.  Maybe this link is relevant?

https://www.mathworks.com/help/matlab/matlab_external/python-dict-variables.html

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System