pvaPy syntax

[Pierrick M Hanlet via Tech-talk <tech-talk at aps.anl.gov>]

I have an IOC which serves the PVs to which I want to read and write.  I run pvaPy in
a python program which is a digital twin (DT).  For scalars, I'm successful in reading
from and writing to the PVs from my IOC.  I'm having trouble, presumably syntax, with
lists and dictionaries.

For my lists, I'm doing:

In accelParams.py, I have a function beam_params() in which:
histx_list = []
histx_list = pvaccess.Channel('WFE:MEBT_PHYS_ALSC:histX')
...
return((...,histx_list,...))

In my DT:
from accelParams import beam_params
...,histx_list,...=beam_params()
...
fill list name histx
...
histx_list.putScalarArray('histx_list','histx','INT')    <<<===== this is line 988

I don't understand the documentation; I thought that I could use the simplest form of this:
histx_list.putScalarArray('histx')

I don't understand the error messages either; they always appear to ask for one more argument
than I provide:
===================================================================================================
Error in main: Python argument types in
     Channel.putScalarArray(Channel, str, str, str)
did not match C++ signature:
     putScalarArray(Channel {lvalue}, boost::python::list valueList)
     putScalarArray(Channel {lvalue}, boost::python::list valueList, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > requestDescriptor)
Traceback (most recent call last):
   File "/home/epics/Simulations/DigitalTwin/MEBT_DT/MEBT_DT_04MAY_2025_v1.py", line 1035, in <module>
     main()
   File "/home/epics/Simulations/DigitalTwin/MEBT_DT/MEBT_DT_04MAY_2025_v1.py", line 988, in main
     histx_list.putScalarArray('histx_list','histx','INT')
Boost.Python.ArgumentError: Python argument types in
     Channel.putScalarArray(Channel, str, str, str)
did not match C++ signature:
     putScalarArray(Channel {lvalue}, boost::python::list valueList)
     putScalarArray(Channel {lvalue}, boost::python::list valueList, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > requestDescriptor)
===================================================================================================

The second question is with regards to connecting a dictionary with a scalar array.  In beam_params(),
I have:
twissx_dict = {}
twissx_dict = pvaccess.Channel('WFE:MEBT_PHYS_ALSC:TwissX').getIntrospectionDict()
Is this what I should be using, or is a simple Channel() sufficient?

Many thanks,
Pierrick



-- 
Pierrick Hanlet
Fermi National Accelerator
Accelerator Front End Controls
+1-630-840-5555 -- lab
+1-312-687-4980 -- mobile

"Whether you think you can or think you can't, you're right" -- Henry Ford