Skip to content

Cyclic execution of Python script

dlabelle@phoenixcontact.cadlabelle@phoenixcontact.ca
edited June 2020 in PLCnext Technology & PLCnext Controls

Hi,

What would be the simplest way to execute a script installed on the PLCnext in a cyclic way?

Example, we have a python script in the PLC that reads variables through REST Data Interface and we want to cyclically execute that script.

Is there a way to call it from the PLC programming (Through PLCnext Engineer)?

Thanks

Robin

Comments

  • Dan ClarkDan Clark

    Robin,

    You can create a loop, see the below example.

    <span style="font-family: monospace;">delay = 100  #100ms</span>

    try:

      print("Press Ctrl+C to stop the script.")
      while 1:
        Inputs = Pullloop()
    <span style="font-family: monospace;">    #(logic here)</span>
        Postloop(Outputs)
        time.wait(delay)
    except KeyboardInterrupt:
      sys.exit()

    You could call it from Engineer, but keep in mind HTTP requests are synchronous (meaning they will not execute the next line of code until it has completed), and the time between pulls would not be as consistent as doing it in the program. 

  • Martin - PLCnext Technology TeamMartin - PLCnext Technology Team

    Hi Robin,

    In the next release of PLCnext Base library - due soon, I think - there will be a "Shell" function that you can call from PLCnext Engineer, which you could use to execute your Python script. Then, you could use an ESM cyclic task to implement the timed calling cycle. This shell command will be executed asynchronously, so it will not hold up the processing of the real-time task.

    ~ Martin.

  • smaher4smaher4
    Hi Martin,
    Was the "shell"function you mentioned ever released?
    I am also looking to execute a python scrip from PLCnext on a timed basis
  • Martin - PLCnext Technology TeamMartin - PLCnext Technology Team
    Yes, the Linux Shell function block is now included in the PLCnextBase library, in the PLCnext Store.
    ~ Martin.
  • malcomvxmalcomvx
    Have a look at threading.Timer. It runs your function in a new thread without using sleep().

    from threading import Timer
    def hello():
    print "hello, world"

t = Timer(30.0, hello)
t.start() # after 30 seconds, "hello, world" will be printed
  • alexaminaralexaminar
    Python sleep() Python sleep() will pause for an hour, day or whatever if given the proper value. It does not allow other processes take place (in same script) however. A better way is to use an event which will create an event on timeout.
Sign In or Register to comment.