# Class object scope issues

**URL:** <https://forum.inductiveautomation.com/t/class-object-scope-issues/12572>\
**Category:** General Discussion\
**Created:** [January 18, 2017, 5:18pm UTC](https://forum.inductiveautomation.com/t/class-object-scope-issues/12572 "2017-01-18T17:18:04Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![dberry](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@dberry](https://forum.inductiveautomation.com/u/dberry)\
**Post date:** [January 18, 2017, 5:18pm UTC](https://forum.inductiveautomation.com/t/class-object-scope-issues/12572/1 "2017-01-18T17:18:04Z")

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I am having some trouble with scoping in Ignition. I am trying to create a persistent class object that I can access from anywhere that is gateway scoped.

I have a script module with a class definition and a couple of functions defined (shared.Simulation):

class myclass:  
Def **init** (self)  
self.y=0  
def startup():  
shared.simulation.x=myclass()  
def run():  
z = shared.simulation.x.y

In a Data Type definition, I have a tag value change script that calls the run function:  
shared.simulation.run()

The startup function needs to get called first.  
If I put the call to startup (instantiates the object “x” in a memory tag (mytag) value change script, I get no error

However, if I instead put that same call to the startup in a Gateway Event script,(tag value change event) and assign the same memory tag (mytag), then I get an error that shared.Simulation has no attribute “x”, and globals() does not contain the class instance I created using the startup function call.

I thought that tag change event scripts were gateway scoped and so I don’t understand why the object does not seem to exist in the same memory space.

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**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [January 18, 2017, 6:09pm UTC](https://forum.inductiveautomation.com/t/class-object-scope-issues/12572/2 "2017-01-18T18:09:25Z")

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[quote=“dberry”]I am having some trouble with scoping in Ignition. I am trying to create a persistent class object that I can access from anywhere that is gateway scoped.[/quote]You are close. Don’t use a startup function. Simply instantiate the class at the top level of your module. (Modules are “initialized” by running them.) Like so:[code]class myclass:  
def **init** (self)  
self.y=0

x=myclass()

def run():  
z = x.y[/code]You should be aware that this startup operation will happen any time any shared script module is edited and saved.  
{ Also, use the “code” annotation in your posts so your readers can see the indents. }

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<div class="post-metadata">

**Author:** ![dberry](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@dberry](https://forum.inductiveautomation.com/u/dberry)\
**Post date:** [January 18, 2017, 7:45pm UTC](https://forum.inductiveautomation.com/t/class-object-scope-issues/12572/3 "2017-01-18T19:45:53Z")

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Thank you for your helpful reply. This did the trick. And thanks for pointing out the “code” annotation.

I guess I still don’t understand why explicitly instantiating the class to the shared.Simulation module from within a function call doesn’t create the object in the same memory space? Does the object only persist until this function completes execution?

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<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [January 18, 2017, 11:50pm UTC](https://forum.inductiveautomation.com/t/class-object-scope-issues/12572/4 "2017-01-18T23:50:54Z")

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[quote=“dberry”]I guess I still don’t understand why explicitly instantiating the class to the shared.Simulation module from within a function call doesn’t create the object in the same memory space? Does the object only persist until this function completes execution?[/quote]Never really thought about it. Only by putting the assignment at the top level can you avoid races between your setup() and run(). A call to run() from outside the script module has to wait for the script module to fully load (execute top to bottom), but won’t necessarily wait for anything else.