Expression Binding Help - Passing list/array/sequence as an argument to a Python Script

Ignition
,
1

I am attempting to run a scrip function in a expression binding. My python function accepts two arguments, both which need to be a list.

Example:
def check(tag1,tag2):
do something
return(some string)

tag1 are ints and tag2 being strings

Expression Binding Language:
runScript(“project.check”,0,[1,1],[‘string1’,‘string2’] )
//This don’t work is it possible to make list in expression language
//I know it possible in latest version of ignition but we are working in prior version.

2

Your syntax is not correct. You may want to pass list or arrays as encode strings.

runScript(“project.check”,0,"[1,1]","['string1','string2']")

Then decode as real object with

import ast
values = "[1,1]"
paths = "['string1','string2']"
values = ast.literal_eval(values)
paths = ast.literal_eval(paths)
3

It might be easier to use a script transform, maybe with an expression structure binding.

edit - ah, didn’t see you’re on 7.9. I don’t know anything about 7.9.

4

I haven’t tried it yet but this should work. But since my strings are in tag paths I would need to use a system.tag.read () to get the string. Thanks

5

Consider using my objectScript function (from Simulation Aids) instead of runScript. runScript() only passes extra expression arguments when the first (string) argument evaluates to a python function.

My objectScript() accepts any python expression as a string, and delivers expression arguments in a local variable. Which means your python expression can listify your arguments without relying on the stringification of your lists. Your attempt with runScript would become this:

objectScript("project.check([args[0], args[1]], [args[2], args[3]])",
	1, 1, 'string1', 'string2')

If project.check accepts list-like objects (such as tuples), not just true lists, that can be simplified with slicing:

objectScript("project.check(args[:2], args[2:])",
	1, 1, 'string1', 'string2')
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