Difference between "with LogixDriver('ip') as plc", and plc = LogixDriver('ip'), pycomm3.exceptions.CommError: A session must be registered before a Forward Open #223

jds8086 · 2022-07-23T18:27:35Z

jds8086
Jul 23, 2022

Can someone explain to me the functional difference between

with LogixDriver('10.52.44.10') as plc:
    print(plc.read('BoilerOneFeedWaterPressure').value)

and

plc = LogixDriver('10.52.44.10')
print(plc.read('BoilerOneFeedWaterPressure').value)

The first works just fine, the second throws the exception:

pycomm3.exceptions.CommError: A session must be registered before a Forward Open

pcwii · 2022-07-23T18:46:02Z

pcwii
Jul 23, 2022

You have a typo in the second one. You're are missing the opening quote for the ip address. Cheers!

2 replies

jds8086 Jul 23, 2022
Author

Thanks, odd that it's there in my ide, so this isn't the issue.

I guess i should add that the root of the issue is that i do not want to use 'with' and have to connect to the plc every time i want to read a tag or set of tags, mainly because of the delay when initially connecting. I want to connect once, then do reads as necessary from there. All of the examples i see are using 'with'

jds8086 Jul 23, 2022
Author

Found .open() in another users post here, it's pretty obvious i guess but i missed that bit. It's working as i wanted it too now (or at least i'm past that roadblock, time to start the real fun)

plc = LogixDriver('10.52.44.10')
plc.open()
print(plc.read('BoilerOneFeedWaterPressure').value)

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Difference between "with LogixDriver('ip') as plc", and plc = LogixDriver('ip'), pycomm3.exceptions.CommError: A session must be registered before a Forward Open #223

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Difference between "with LogixDriver('ip') as plc", and plc = LogixDriver('ip'), pycomm3.exceptions.CommError: A session must be registered before a Forward Open #223

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