There's a method on the iris.gref class called "data".

set ^zJES(1)="$data = 1"
set ^zJES(2,0)="$data = 10"
set ^zJES(4) = ""
set ^zJES(4,0) = ""

The result ends up matching $data:

>>> glb = iris.gref("^zJES") 
>>> print(glb.data())
10
>>> print(glb.data([1])) 
1
>>> print(glb.data([2]))
10
>>> print(glb.data([3]))
0
>>> print(glb.data([4]))
11

I found running help(iris) at the Python shell helpful for working this kind of stuff out.

Edit: Unlike @Robert Cemper's solution this does not return the value of the node we're testing (like the 2 parameter usage $data)

You can also try overriding the GUIDENABLED parameter from %Persistent:

Class User.Test1 Extends %Persistent

{

Parameter GUIDENABLED = 1;

Property Property1 as %String;

Storage Default

{

<Data name="Test1DefaultData">

<Value name="1">

<Value>%%CLASSNAME</Value>

</Value>

<Value name="2">

<Value>Property1</Value>

</Value>

</Data>

<DataLocation>^User.Test1D</DataLocation>

<DefaultData>Test1DefaultData</DefaultData>

<IdLocation>^User.Test1D</IdLocation>

<IndexLocation>^User.Test1I</IndexLocation>

<StreamLocation>^User.Test1S</StreamLocation>

<Type>%Library.CacheStorage</Type>

}


}

Will give you:

USER>set obj = ##class(Test1).%New()

USER>set obj.Property1 = "Hello"

USER>w obj.%Save()

1

USER>w obj."%%GUID"

FC381F94-277E-11E8-82F0-005056B479AA

The ^OBJ.GUID index that this creates can be accessed via %ExtentMgr.GUID.