arcpy - Changing Parameter Type from Optional to Required in Python Toolbox?

I am creating a Python toolbox with 5 parameters. One of the parameters is a Boolean/checkbox, which checks if the user wants to edit the labels of a shapefile. What I would hope to do is if the user enables this checkbox, then change the parameter type of two of my other parameters to be required.

Is there a simple way to do this?

For the time being, my toolbox looks like the following:

If "Edit Labels?" is checked, I would like Label Font Size and Bold Font to be changed to be required inputs. I tried to do this within the updateParameters() method, but it seems like that is only used once the "OK" button is hit.

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Here is the code that I have been working on:

import arcpy


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

        # List of tool classes associated with this toolbox

        self.tools = [applyMultipleLayerFeatures]

class applyMultipleLayerFeatures(object):
    def __init__(self):
        """Define the tool (tool name is the name of the class)."""
        self.label = "Apply Multiple Layer Features"
        self.description = "Applies features to multiple layers. Customize a single layer and use it as a source layer in the tool then select layers to be modified by the tool"
        self.canRunInBackground = False

    def getParameterInfo(self):

        """Define parameter definitions"""

        # First parameter = layer with customized features
        param0 = arcpy.Parameter(
            displayName = "Source layer with customized features",
            name = "source",
            datatype = "Feature Layer",
            parameterType = "Required",
            direction = "Input")


        # Second parameter = layers to which customized features will be applied
        param1 = arcpy.Parameter(
            displayName = "Layers with features to be updated",
            name = "updlayers",
            datatype = "GPValueTable",
            parameterType = "Required",
            direction = "Input")

        param2 = arcpy.Parameter(
            displayName = "Edit labels?",

            name = "enableLabels",
            datatype = "GPBoolean",
            parameterType = "Required",            
            direction = "Input")             

        param3 = arcpy.Parameter(
            displayName = "Label Font Size",
            name = "labelFontSize",
            datatype = "GPDouble",
            parameterType = "Required",            

            direction = "Input")

        param4 = arcpy.Parameter(
            displayName = "Bold Font:",
            name = "labelBoldFont",
            datatype = "GPBoolean",
            parameterType = "Required",            
            direction = "Input")            

        param1.columns = [['Feature Layer', 'Features']]       


        params = [param0, param1, param2, param3, param4]

        return params

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

    def updateParameters(self, parameters):

        if parameters[2].value:
            parameters[3].parameterType = "Required"
            parameters[4].parameterType = "Required"
        else:
            parameters[3].parameterType = "Optional"
            parameters[4].parameterType = "Optional"
        return       

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


        #Get Inputs

        for input in parameters:
            arcpy.AddMessage("This is part of the parameters list:" + input.name)

        updlayers = parameters[1].values
        enableLabels = parameters[2].value
        labelFontSize = parameters[3].value
        labelBoldFont = parameters[4].value       


        if enableLabels == True:        
            for layers in updlayers:
                for labels in layers:
                    labels.showLabels = True
                    if labelBoldFont == True:
                        for a in labels.labelClasses:
                            a.expression = '"%s" + [Name] + "%s"' %  ("","")
                    else:
                        for a in labels.labelClasses:

                            a.expression = '"%s" + [Name] + "%s"' %  ("","")

        source = parameters[0].valueAsText
        updlayers = parameters[1].valueAsText.split(";")

        for app in updlayers:
            arcpy.ApplySymbologyFromLayer_management(app.strip("'"),source)

        arcpy.RefreshTOC
        arcpy.RefreshActiveView

        return

Answer

updateParameters() is called whenever any parameter's value is changed. You should be able to use a function like the following:

def updateParameters(self, parameters):
    if parameters[2].value:
        parameters[3].parameterType = 'Required'
        parameters[4].parameterType = 'Required'
    else:
        parameters[3].parameterType = 'Optional'
        parameters[4].parameterType = 'Optional'

    return

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EDIT: It turns out that parameterType is a read-only property. Given that, I'm not sure that what you're asking is actually possible. Perhaps it's best to initialize them with parameterType='Required', set default values for the parameters after initialization (e.g. param3.value=0 and param4.value=False), and then simply ignore them if the box is unchecked.

Another option would be to initialize the parameters as required, then enable/disable them based on the checkbox value. I haven't tested for myself whether an unspecified disabled required parameter will give you an error, but the code to try would be:

def updateParameters(self, parameters):
    if parameters[2].value:
        parameters[3].enabled = True
        parameters[4].enabled = True
    else:

        parameters[3].enabled = False
        parameters[4].enabled = False
    return