Experimental Physics and
Industrial Control System

Hi Matt,

On Apr 15, 2021, at 10:47 AM, Matt Newville wrote:
>
> You could just write a simple plain python script that performed some action when the PV changed by button push happened.   That can be as simple as
>
> while True:
>     epics.poll(0.025)
>     if epics.caget('button_push'):
>        do_something()


Does pyepics use a CA monitor behind the scenes to implement that epics.caget() call? If it doesn't that example would be hitting the IOC with a get at up to 40Hz, which isn’t something I’d recommend. I’m guessing it probably does which is fine when using pyepics, but translating the above code into some other scripting language and calling the caget program from Base in a fast loop like that would not be advisable.

Just wanting to make sure readers understand if there is some magic going on there!

- Andrew


> A slightly more complex version, using a pyepics Device might look like the script below.   This assumes there is a set of pre-defined PVs that control the calculation/work to be done and that these are loaded into an IOC.  That is different for pcaspy, where the PVs could be defined on the fly (but then you have to figure out how the Display Manager exposes them).
>
> It really isn't very much different from a seq state-notation program except that the PVs live in a soft IOC and the logic happens in a separate process.  This approach allows the logic of the program to be in python and can be changed without restarting the IOC (or the sequence process in the IOC).   The trade-off is that the script needs to be running in addition to the IOC.  procServ or screen can help with that. 
>
> ####
> import numpy as np
> import epics
>
> DSPACES = {'Si': 5.4309, 'Ge': 5.658}
> HC = 12398.419
>
> class Analyzer(epics.Device):
>     "Simple Device to set analyzer angle from energy, crystal, h, k, l"
>     attrs = ('go_button', 'energy',
>              'h', 'k', 'l', 'xtal', 'theta', 'moving')
>     _nonpvs = ('_prefix', '_pvs', '_delim', 'do_calc', 'en_val')
>
>     def __init__(self, prefix='Analyzer:'):
>         epics.Device.__init__(self, prefix, attrs=self.attrs)
>         self.needs_calc = 0
>         self.moving = 0
>         self.add_callback('go_button', self.onButtonPush)
>
>     def onButtonPush(self, value, **kws):
>         self.needs_calc = True if value == 1 else False
>
>     def do_work(self):
>         self.go_button = 0
>         self.moving = 1  # Set "in progress"
>
>         ## real code here:
>         xtal_name = self._pvs('xtal').get(as_string=True)
>         dspace = DSPACES[xtal_name]
>         hkl    = np.array([self.h, self.k, self.l])
>         theta  = np.arcsin(np.sqrt(hkl**2).sum() * HC/(2*dspace*self.energy))
>
>         self._pvs['theta'].put(theta, wait=True)
>         self.moving = 0  # Set "not in progress"
>
>     def run(self):
>         while True:
>             epics.poll(0.05)
>             if self.needs_calc:
>                 self.do_work()
>
> if __name__ == '__main__':
>     Analyzer(prefix='XXAnalyzer:').run()
> ####
>
> Slightly off-topic, but for clarity here: pyepics Devices will map the PV "prefix" and "suffix" to Python variable names, so that in the code below, using prefix='XXAnalyzer:' assumes that the PVs are named 'XXAnalyzer:go_button' (probably a 'bo')  'XXAnalyzer:energy', 'XXAnalyzer:h', 'XXAnalyzer:k', and so on. Those will get mapped in the code so that reading or writing to "self.h" will really connect to and get()/put() the PV value, or you can get to the real pyepics PV object with "self._pvs['energy']", which is needed to do things like setting a (monitor) callback, getting the string representation of the value, or doing a put with a simple callback to wait for the processing to complete.
>
> Anyway, that's all to say that it is possible to have a "plain" pyepics script that reacts to a button push on a Display Screen that then does some non-trivial calculation (or triggers some motor movement or detector, etc).
>
> --Matt
>
>
>
> On Thu, Apr 15, 2021 at 12:59 AM Manoussakis, Adamandios via Tech-talk <tech-talk at aps.anl.gov> wrote:
> Hi Kay,
>
> 
>
> Thanks for the link, I tried adding to my settings.ini file but still doesn’t seem to be finding the packages I am importing in my script (pandas, numpy).
>
> 
>
> org.csstudio.display.builder.runtime/python_path=C:\Users\PC\AppData\Local\Programs\Python\Python39\
>
> 
>
> I did find a fairly old post by you on tech talk and was wondering if this still applied to Phoebus/Jython (seems like jython still doesn’t work with numpy from looking around)
>
> 
>
> “CSS BOY scripts are executed in jython, not python.
>
> Most of the default python modules are also available in jython, but when you install python modules with binary dependencies like numpy, MySQL_python, .. those are not available in jython.”
>
> 
>
> If this is the case, it seems like I might have to go the pythonIoc route but I really just wanted to have the script get called when a pv changed value (was using the button to write a value change causing the script to trigger).
>
> 
>
> 
>
> 
>
> Thanks,
>
> Adam
>
> 
>
> 
>
> 
>
> 
>
> 
>
> 
>
> From: Kasemir, Kay <kasemirk at ornl.gov>
> Sent: Wednesday, April 14, 2021 10:41 AM
> To: tech-talk at aps.anl.gov; Manoussakis, Adamandios <manoussakis1 at llnl.gov>
> Subject: Re: Python Script call from Button press, module not found
>
> 
>
> See python_path in https://control-system-studio.readthedocs.io/en/latest/preference_properties.html#display-builder-runtime
>
> 
>
>

--
Complexity comes for free, simplicity you have to work for.