Re: pypva, PvObject and NTTable

["Veseli, Sinisa via Tech-talk" <tech-talk at aps.anl.gov>]

Hi,

I want to use a different number of columns depending upon the user configuration.

I have the following queries

1) Can I change the structDict to another struct2Dict and update the PV. The API getIntrospectionDict or getStructureDict can only get the existing structure. Is there any API to modify/update the structure of the pv object at runtime?

You cannot change record structure definition at runtime, but you can easily remove old record and add new one:

>>> from pvapy import *

>>> nt = NtTable(3, DOUBLE)

>>> print(nt)

epics:nt/NTTable:1.0

    string[] labels []

    structure value

        double[] column0 []

        double[] column1 []

        double[] column2 []

    string descriptor

    alarm_t alarm

        int severity 0

        int status 0

        string message

    time_t timeStamp

        long secondsPastEpoch 0

        int nanoseconds 0

        int userTag 0

>>> s = PvaServer()

>>> s.addRecord('t', nt)

>>> c = Channel('t')

>>> pv = c.get()

>>> print(pv)

structure

    structure value

        double[] column0 []

        double[] column1 []

        double[] column2 []

>>> nt2 = NtTable(5, INT)

>>> s.update('t', nt2)

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

ValueError: structure definitions do not match

>>> s.removeRecord('t')

>>> s.addRecord('t', nt2)

>>> pv = c.get()

>>> print(pv)

structure

    structure value

        int[] column0 []

        int[] column1 []

        int[] column2 []

        int[] column3 []

        int[] column4 []

2) In the epics:nt/NTTable:1.0" object all the columns should have the same number of elements/rows. Is it possible to have different number elements/rows in different columns. Presently I am filling the empty ones with null string.

Yes, something like this will work:

>>> nt2.setColumn(1, [1,2,3])

>>> nt2.setColumn(2, [1,2,3,4,5,6])

>>> print(nt2)

epics:nt/NTTable:1.0

    string[] labels []

    structure value

        int[] column0 []

        int[] column1 [1,2,3]

        int[] column2 [1,2,3,4,5,6]

        int[] column3 []

        int[] column4 []

3) Is it possible to have the number of columns of the NTTable PvObject  to be programmable at run time. similar to as in C functions printf(char*, ...)

Yes, you can add/remove records at runtime, and hence you can change it however you like.

I hope this helps,

Sinisa

--

Siniša Veseli

Scientific Software Engineering & Data Management

Advanced Photon Source

Argonne National Laboratory

sveseli at anl.gov

(630)252-9182

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Kuldeep Joshi via Tech-talk <tech-talk at aps.anl.gov>
Sent: Thursday, August 11, 2022 6:35 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: pypva, PvObject and NTTable

 

2) In the epics:nt/NTTable:1.0" object all the columns should have the same number of elements/rows. Is it possible to have different number elements/rows in different columns. Presently I am filling the empty ones with null string.

Regarding this point, it seems the limitation is due to the Phoebus table widget.

On Thu, Aug 11, 2022 at 4:55 AM Kuldeep Joshi <kuldeep.joshi at gmail.com> wrote:

Hello,

I am using a pypva server and publishing a NTTable object. This object is being displayed using the table widget of phoebus

   tablePV = PvObject(structDict, "epics:nt/NTTable:1.0")

I want to use a different number of columns depending upon the user configuration.

I have the following queries

1) Can I change the structDict to another struct2Dict and update the PV. The API getIntrospectionDict or getStructureDict can only get the existing structure. Is there any API to modify/update the structure of the pv object at runtime?

2) In the epics:nt/NTTable:1.0" object all the columns should have the same number of elements/rows. Is it possible to have different number elements/rows in different columns. Presently I am filling the empty ones with null string.

3) Is it possible to have the number of columns of the NTTable PvObject  to be programmable at run time. similar to as in C functions printf(char*, ...)

Presently I am deleting the PvObject and adding one with modified the structure Dictionary.

Thank you in advance.

Regards,

Kuldeep