Determining if connection is lost about pylogix HOT 11 CLOSED

I would say that it has been improved since the addition of returning the Response class. If you are actively reading something in a loop, then suddenly the PLC is no longer available, you will initially receive "Connection Lost" as the status. The problem then is that the next read, it will try to reconnect and will fail. If you use a try/catch around your read, it will reconnect once the PLC is available.

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There is definitely room for improvement on error handling on my part. For now, if you are only reading every few minutes, I'd do your reads, then close the connection by calling .Close(). Even though you are probably not currently closing the connection, the PLC will purge connections after a period of inactivity.

I'll see what improvements I can make.

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No problem. I just wanted to make sure that I wasn't overlooking something.

If I come up with a solution I'll let you know.

Thanks!

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Has anyone made progress on this issue? My python is pretty limited, but I'm thinking of jumping into this. My application is a 4-line text display replacement. So it's pretty simple. The issue is that the my users need some indication that the system is no longer communicating.

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Excellent. I just added try/except and it works perfectly. If I were a little more experienced with python I guess I would have known to try that.

For my simple application this is probably all I'll ever need in the way of comm loss detection.

Thank you!

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Excellent. I just added try/except and it works perfectly. If I were a little more experienced with python I guess I would have known to try that.

For my simple application this is probably all I'll ever need in the way of comm loss detection.

Thank you!

Can you please upload and commit? Or give an example?

Thanks in advance.

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@marne44

Try/Catch is a concept in all programming languages. Have a look in my repo file below line 158 for an example of try catch. Basically what happens is that it tries to do the code inside the try, if it gets an exception then the code inside the exception gets executed. There's another one finally, for clean up too.

https://github.com/kodaman2/Data_Preserve/blob/master/data_preserve.py

Docs: https://docs.python.org/3/tutorial/errors.html

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This is what's working for me...

def UpdateValue():
    try:
        retL = comm.Read(tagList1)
        myapp.commerror=FALSE
    except:
        myapp.commerror=TRUE

    ### ... continue processing valid results

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What will the value of tag be when it gets "Connection Lost" Status?

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What will the value of tag be when it gets "Connection Lost" Status?

Should be None

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In my application, the code that uses the tag values is notified that myapp.commerror=TRUE. At that point I can decide what's more appropriate - hold previous tag values, or zero the tag values.

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