Writing to Tags

Ignition
, ,
1

Hi. I am trying to write from a list of tags and write to another list. Here is the code I am using:

paths = [
	"[ABC]Building 4/PCP/Remote Sites Bridge/Location1/Bridge_Location1_0_",
	"[ABC]Building 4/PCP/Remote Sites Bridge/Location1/Bridge_Location1_1_"
	]
	
	
values = [
	"[Remote Sites]Location1/Tank 1",
	"[Remote Sites]Location1/Tank 2"
	]
	
system.tag.writeBlocking(paths, values)

When using that I get the following error
[Error_TypeConversion("Error trying to coerce '[Remote Sites]Location1/Tank 1' to a number."), Error_TypeConversion("Error trying to coerce '[Remote Sites]Location1/Tank 2' to a number.")]

I have also tried:

paths = [
	"[ABC]Building 4/PCP/Remote Sites Bridge/Location1/Bridge_Location1_0_",
	"[ABC]Building 4/PCP/Remote Sites Bridge/Location1/Bridge_Location1_1_"
	]
	
	
values = [
	"[Remote Sites]Location1/Tank 1".value,
	"[Remote Sites]Location1/Tank 2".value
	]
	
system.tag.writeBlocking(paths, values)

That returns this error:Traceback (most recent call last):
File "", line 7, in
AttributeError: 'str' object has no attribute 'value'

paths = [
	"[ABC]Building 4/PCP/Remote Sites Bridge/Location1/Bridge_Location1_0_",
	"[ABC]Building 4/PCP/Remote Sites Bridge/Location1/Bridge_Location1_1_"
	]
	
	
values = [
	"[Remote Sites]Location1/Tank 1".valueCurrent.value,
	"[Remote Sites]Location1/Tank 2".valueCurrent.value
	]
	
system.tag.writeBlocking(paths, values)```

That also gave me an error.

I am sure I am making a stupid mistake, I just don't know what it is and I have been at this way longer than I should have been.
Thanks

2

You need to first read the [Remote Sites] tags and put them into a variable.

tags = system.tag.readBlocking(remoteSitesPaths)

Then you can write those values to your tags. tags[0].value, tag[1].value, etc.

What you're doing is just writing a string to a tag that is probably a real/int.

2 Likes
3

Something like

#paths to tags to be written
write_paths = [
	"[ABC]Building 4/PCP/Remote Sites Bridge/Location1/Bridge_Location1_0_",
	"[ABC]Building 4/PCP/Remote Sites Bridge/Location1/Bridge_Location1_1_"
	]
	
#path to tags to be read
read_paths = [
	"[Remote Sites]Location1/Tank 1",
	"[Remote Sites]Location1/Tank 2"
	]

#read tags
read_Qvalues = system.tag.readBlocking(read_paths)

#get value from qualified values (optional)
read_values = [Qvalue.value for Qvalue in read_Qvalues]


#write values to tags
system.tag.writeBlocking(write_paths, read_values)

#write values to tags (if values are not extracted from the qualified values)
#system.tag.writeBlocking(write_paths, read_Qvalues)
1 Like
4

kyler.kamyszek and amarks

Thank You. I got it working, but I am not sure why mine didn't. Maybe my head is up my a&& today.

Following the code in the manual:

# Create a List of Tag Paths to write to
paths = ["Scripting/Tags/Alarm_Setpoint_1", "Scripting/Tags/Alarm_Setpoint_2"]
 
# Create a List of values to write
values = [72, 72]
 
# Send of the write requests
system.tag.writeBlocking(paths, values)

I assumed that if I used the

"[Remote Sites]Location1/Tank 1"
or
"[Remote Sites]Location1/Tank 1".value
or
"[Remote Sites]Location1/Tank 1".valueCurrent.value
one of them would have returned the value.

Once again, thanks for you help

5 
paths = [
	"[ABC]Building 4/PCP/Remote Sites Bridge/Location1/Bridge_Location1_0_",
	"[ABC]Building 4/PCP/Remote Sites Bridge/Location1/Bridge_Location1_1_"
	]
	
	
values = [
	"[Remote Sites]Location1/Tank 1".valueCurrent.value,
	"[Remote Sites]Location1/Tank 2".valueCurrent.value
	]
	
system.tag.writeBlocking(paths, values)```

I would expect this line

"[Remote Sites]Location1/Tank 2".valueCurrent.value

to throw an error as a "[Remote Sites]Location1/Tank 2" is just a string and would have no attribute "valueCurrent.value"

**edit: that's exactly the error it produced

Your issue is that "[Remote Sites]Location1/Tank 2" has nothing to do with a tag. Python has no idea what a tag is. You have to use system.tag.readBlocking() to get the value of a tag. To Pyhton, that's just a string. Same as any other string.

With this code you will always be writing the value 72 to those 2 tags. If your goal is to write the value of 2 other tags to these tags you'll need to read those first and then use those read values in your values list.

1 Like
6

Thank you for the explanation. It is appreciated. It's making sense now......
Now on to Google'n the "for....in" that you used so I understand just how that works....

7

List comprehension in Pyhton.

basically this:

read_Qvalues = system.tag.readBlocking(read_paths)

read_values = []
for Qvalue in read_Qvalues:
    read_values.append(Qvalue.value)

becomes this:

read_Qvalues = system.tag.readBlocking(read_paths)

read_values = [Qvalue.value for Qvalue in read_Qvalues]

It just creates the list and assigns it all on one line. I've used chat gpt quite a bit to help me rewrite my loops into list comprehension and it's helped me understand how it works. It's not terrible to read, but it does take some practice to be able to write it from scratch.

3 Likes
8

Or just to be really pedantic

read_Values = [Qvalue.value for Qvalue in system.tag.readBlocking(readPaths)]
1 Like
9

You don't need to extract the values, system.tag.write* functions can take a list of qualified values.

What is the trigger of this tag write ?
If you just want to copy the values from one tag to another, you could use a reference tag and get rid of all scripting.

2 Likes
10

Was not aware of that. That simplifies the script a bit.

1 Like
11

You can force a tag quality with this.

12

I am using it in a Gateway Event Timer Script

More of less, I need to copy the value from some MQTT tags into a PLC that is connected to two different networks.... (don't ask. Corporate IT overlords.....)

13

Then unless the timer has any kind of importance, or the destination tags need to stay memory tags because reasons, get rid of the event script and use reference tags.

3 Likes
14

It's also possible to do a tag -> tag sync via transaction groups, if you want another way to avoid scripting. If the end result doesn't need to be a memory tag though, definitely reference tags are the way to go.