[GIS] Using Global Variables in Python Toolbox

Question

How do I create a global variable in a python toolbox?

The eventual purpose is that I would like to store information related to the execution of my script across functions, but not as "parameters". They might be boolean, or dictionaries, but in my example below, I am using a "String for simplicity.

Add text to the Something parameter, move to Something Else, and click Ok.
On execution, the value of self.whatever is added to the messages in ArcCatalog. It's the initial value of "ABC".

import arcpy    

class Toolbox(object):
    def __init__(self):
        """Define the toolbox (the name of the toolbox is the name of the
        .pyt file)."""
        self.label = "Toolbox"
        self.alias = ""

        # List of tool classes associated with this toolbox
        self.tools = [Tool]

class Tool(object):
    def __init__(self):
        """Define the tool (tool name is the name of the class)."""
        self.label = "Tool"
        self.description = ""
        self.canRunInBackground = False
        self.whatever = "ABC"

    def getParameterInfo(self):
        """Define parameter definitions"""

        param0 = arcpy.Parameter(
            displayName="Something",
            name="something",
            datatype="GPString",
            parameterType="Required",
            direction="Input"
        )

        params = [param0]

        return params

    def isLicensed(self):
        """Set whether tool is licensed to execute."""
        return True

    def updateParameters(self, parameters):
        """Modify the values and properties of parameters before internal
        validation is performed.  This method is called whenever a parameter
        has been changed."""

        self.whatever = "XYZ"

        return

    def updateMessages(self, parameters):
        """Modify the messages created by internal validation for each tool
        parameter.  This method is called after internal validation."""
        return

    def execute(self, parameters, messages):
        """The source code of the tool."""

        arcpy.AddMessage("The value whatever is: " + self.whatever)

        return

Answer 1

Just write:

import arcpy    
aGlobal = None

class aClass():
    aMethod(self):
        global aGlobal
        aGlobal = self.whatever

Without the global statement it will be local inside the method. Alternatively you can set a non-self variable inside the class, which I think survives the object life cycle.