Globally Accessible Variable

[Devin_Golberg]

I know I'm approaching this incorrectly, but I'm not quite sure how to go about this in Ignition and I'm struggling to come up with the right search criteria to find it, somehow...

What I'd like to do is create a class object on one button press and then access that stored object in another button press.

I currently have a test project script (UniversalScripts.TestScripts) setup as follows:

class TestClass:
	def __init__(self):
		self.reply = "Hello World!"

	def setReply(self,rep):
		self.reply = rep

	def getReply(self):
		return self.reply

In button 1 I have:

test = UniversalScripts.TestScripts.TestClass()
test.setReply("This is a reply")
print test.getReply()

Which obviously prints the stated reply to the console. In button 2 I have just:

print test.getReply()

which obviously returns an error because it's not been initialized under button 2, only inside of button 1.

Where would I store the "test" variable from button 1 so that I can access the same instance of it from within button 2? If I try to store it in a script, I still get a different instance of the variable in button 2 vs button 1 (which I expect). Doing this in Java, I could just store the variable in the parent class that creates the buttons and access it that way, but I don't know what would be considered the parent class, in this case (the parent container?) nor how to store/access a variable there from within a button.

I feel like this should be obvious to me, but it's been a long day (week really) and my brain feels like mush, so... Help!

[pturmel]

You can create collection objects as top-level variables in a script module, and any keys you assign to them will be available throughout the JVM for that project. True in all scopes (but separate by JVM, and separate by project in the gateway).

You can also use the standard Java Swing .putClientProperty() and .getClientProperty() methods on components and windows in Vision.

[Devin_Golberg]

Thank you! That helped a lot! I came up with the below code to get it to work between buttons:
Project Script:

global tClass

def getTestClass():
	return tClass

class TestClass:
	def __init__(self):
		self.reply = "Hello World!"

	def setReply(self,rep):
		self.reply = rep

	def getReply(self):
		return self.reply

Button 1:

UniversalScripts.TestScripts.tClass = UniversalScripts.TestScripts.TestClass()
test = UniversalScripts.TestScripts.getTestClass()
print test.getReply()
test.setReply("Test Reply")
print test.getReply()

Button 2:

test = UniversalScripts.TestScripts.getTestClass()
print test.getReply()
test.setReply("New Reply")
print test.getReply()

Which prints out:

Hello World!
Test Reply
Test Reply
New Reply

It almost feels TOO simple! Thank you! This will do exactly what I need it to!

Does this look like the "correct" way to be doing this, or should I alter it in any way? I'm a Python/Jython/Ignition newbie here, so...

[pturmel]

@Devin_Golberg

should I alter it in any way

Yes.

• The global keyword has no meaning at the top level. It is intended to be used in functions and methods to make assignment to a top level variable possible from within those functions or methods. You don't need it in this case.

• Instead, assign to tClass to initialize it at the top level of the script (outside any function). Then you do not need the getTestClass() method, as it is equivalent to simply referencing path.to.package.tClass.

• Using a class object instead of a native collection will complicate your life greatly if you need cross-project sharing in gateway scope.

[Devin_Golberg]

@pturmel

• The global keyword has no meaning at the top level. It is intended to be used in functions and methods to make assignment to a top level variable possible from within those functions or methods. You don't need it in this case.

• Instead, assign to tClass to initialize it at the top level of the script (outside any function). Then you do not need the getTestClass() method, as it is equivalent to simply referencing path.to.package.tClass.

Ahh, I think I was trying to assign to tClass from within a function without using global is why it wasn't working for me the way I initially tried it (getters/setters habit from Java and not knowing about global definition). I probably also forgot that you have to assign the new class to the variable after the class definition or it doesn't recognize that the class exists. IIRC, you could assign a class to a variable on a line before the class is even defined and it will still work, in JavaScript (been a while), whereas Python seems more strict in that regard, requiring that the class be defined before it can be called for assignment.

@pturmel

• Using a class object instead of a native collection will complicate your life greatly if you need cross-project sharing in gateway scope.

For this use-case, I just need it within the client scope, but this is good information for the future, as I'll likely try something along those lines as I get more into Ignition.

Thank you again!