Validator error with lists and set values

Question

I have some simple ArcPy script tool validator code that is giving me grief. I am using desktop at 10.3.1. I'm open to whatever help can be offered to get this to work as intended. I have two parameters for my script tool. The first is the type of product to be created, the second is the scale of the product. Digital Map / No scale required are the default values defined in the Tool Validator code. If it is a paper product, the user selects the appropriate scale from the drop-down list. The problem I can't solve is that if the user changes the value in parameter 0 to paper map, the list of scales becomes available but the value is still the default ("No scale required") so an error is thrown because that option is not in the scale list. The error clears when I select the scale from the list, but I want only those choices available and obviously don't want the error to appear at all. Likewise if I then change parameter 0 back to Digital Map the "No scale required" value appears but the error message is thrown again because that value is not in the scale list, which is somehow still appearing. There is no way to clear the error at this point. I'd really appreciate help with how to get these different combinations to appear and change as intended without any errors. If they pick Paper, only the scales appear. If they switch back to Digital, only the "No scale required" value appears. And so on. I can't guarantee the user's behaviour so I'd like for it to be bulletproof. import arcpy class ToolValidator(object): def __init__(self): self.params = arcpy.GetParameterInfo() def initializeParameters(self): # Define the list of product types the user can choose from self.params[0].filter.list = ["Digital Map", "Paper Map"] self.params[0].value = "Digital Map" return def updateParameters(self): if self.params[0].value == "Digital Map": self.params[1].value = "No scale required" if self.params[0].value == "Paper Map": self.params[1].filter.list = ["1:10,000", "1:25,000"] return def updateMessages(self): return‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

RandyBurton · Accepted Answer

Try the following for the tool validator: import arcpy class ToolValidator(object): def __init__(self): self.params = arcpy.GetParameterInfo() def initializeParameters(self): return def updateParameters(self): if self.params[0].value == None: self.params[0].value = "Digital Map" if self.params[0].valueAsText == "Digital Map": self.params[1].filter.list = ["No scale required"] else: self.params[1].filter.list = ["1:10,000", "1:25,000"] if self.params[1].value not in self.params[1].filter.list: self.params[1].value = self.params[1].filter.list[0] return def updateMessages(self): return‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ For testing, I used Desktop 10.5. I set the script tool parameters as type string, and populated the map type filter with the digital or paper map options. I did not set the filter list for the map scale. I find it a little easier to use a Python toolbox. You don't have to go to the properties dialog box to edit a tool validator; everything fits into one script. My test version: import arcpy class Toolbox(object): def __init__(self): self.label = "Toolbox" self.alias = "" self.tools = [Tool] class Tool(object): def __init__(self): self.label = "Tool" self.description = "" self.canRunInBackground = False def getParameterInfo(self): MapType = arcpy.Parameter( displayName="Map Type", name="MapType", datatype="String", parameterType="Required", direction="Input") MapType.filter.list = ["Digital Map", "Paper Map"] MapType.value = "Digital Map" MapScale = arcpy.Parameter( displayName="Map Scale", name="MapScale", datatype="String", parameterType="Required", direction="Input") MapScale.filter.list = ["No scale required"] MapScale.value = "No scale required" params = [MapType, MapScale] return params def isLicensed(self): 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.""" if parameters[0].valueAsText == "Digital Map": parameters[1].filter.list = ["No scale required"] else: parameters[1].filter.list = ["1:10,000", "1:25,000"] if parameters[1].value not in parameters[1].filter.list: parameters[1].value = parameters[1].filter.list[0] return def updateMessages(self, parameters): return def execute(self, parameters, messages): """The source code of the tool.""" return‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ Hope this helps.