Struggling with python toolbox tools and parameter validation. updateParameters and updateMessages don't "work"

Glasnoct

I'm currently acquainting myself with the parameter and parameter validation methods of the tool class and I can't quite figure out what's required to get error/warning messages to properly populate and how updateParameters and updateMessages differ for setErrorMessage/setWarningMessage. Either I get no message, the message doesn't update on value change, or its the wrong one. What is the correct code to make sure that a parameter is properly validated after it changes and then displays the proper message (if any)?

For a simple example, I just want to validate that a given parameter is in a list of strings:

 

project_ids = ['123', '456', '789']

class tool:
    def __init__(self):
        """Define the tool (tool name is the name of the class)."""
        self.label = 'test tool'
        self.description = "test"

    def getParameterInfo(self) -> list:
        """Define the tool parameters."""
        project_id = arcpy.Parameter(name="project ID",
                                     displayName="project ID",
                                     datatype="GPString",
                                     parameterType="Required",  # Required|Optional|Derived
                                     direction="Input",  # Input|Output
                                     )
        return [project_id]


    def isLicensed(self):
        """Set whether the 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."""
        if parameters[0].altered:
            if parameters[0].value is None:
                parameters[0].setErrorMessage("No Project Specified")
            elif parameters[0].valueAsText not in project_ids:
                parameters[0].setErrorMessage('Unrecognized project ID')
        return

    def updateMessages(self, parameters):
        """Modify the messages created by internal validation for each tool
        parameter. This method is called after internal validation."""
        # The only time I got messages to show up was when I put the code block from updateParameters here
        return

    @staticmethod
    def execute(self, parameters, messages=None):
        """The source code of the tool."""

        project_id = parameters[0]
        test_function(project_id)
        return

    def postExecute(self, parameters):
        """This method takes place after outputs are processed and
        added to the display."""
        return

 

Hayden Welch

Why are you using updateMessages and updateParameters for this? You can specify a value list in the parameter definition:

 

 

import arcpy

class Tool(object):
    def __init__(self):
        """Define the tool (tool name is the name of the class)."""
        self.label = 'test tool'
        self.description = "test"
        self.project_ids = ['123', '456', '789']

    def getParameterInfo(self) -> list:
        """Define the tool parameters."""
        project_id = \
            arcpy.Parameter(
                name="project ID",
                displayName="project ID",
                datatype="GPString",
                parameterType="Required",  # Required|Optional|Derived
                direction="Input",  # Input|Output
        )
        project_id.filter.type = "ValueList"
        project_id.filter.list = self.project_ids
        return [project_id]
    
    def execute(self, parameters, messages) -> None:
        """Execute the tool."""
        project_id = parameters[0].value
        arcpy.AddMessage(f"project_id: {project_id}")
        return

 

 

If you have more checks you need to do and actually need the updateMessages to return a more specific message to the user, then @BlakeTerhune 's or @AlfredBaldenweck's answers are the way to  go, but avoiding those functions is totally valid if you can enforce the filter in the parameter definition.

Addendum: for some reason, the .altered value of a parameter is not reliable. I've never had luck getting it to work. The best way is to skip checking for altered status and just stick with checking the value. I think this is because Arcpy re-initializes the Parameter objects frequently and sets altered to False by default. You can emulate this by storing the state of the parameters outside the tool object and checking against this 'cache' if you have expensive validation methods.