Populate two columns of a value table parameter with field names derived from two other parameters

[MattHowe]

I'd like to populate two columns of a table of values string parameter in a custom Python tool (non Python toolbox) with fields names from two other parameters. In the example, the first column would have a list of fields from parameter 0, and the second column a list of fields from parameter 1. I only have the option of choosing one dependency in the parameter list (of which works great) but I also need the other parameter. How should Value Table parameters be handled in the validation script so each column's filter list can be defined?

    def updateParameters(self):
        # Modify parameter values and properties.
        # This gets called each time a parameter is modified, before 
        # standard validation.
        if self.params[0].altered and self.params[0].value:
            source_field_list = [f.name for f in arcpy.ListFields(self.params[0].value)]
        if self.params[1].altered and self.params[1].value:
            target_field_list = [f.name for f in arcpy.ListFields(self.params[1].value)]      
        return

This gets the two field lists but just need to figure out how to give them as options in both columns.

[MattHowe · Accepted solution]

Figured it out. I'd set the individual column data types to field when they should have been strings then set the filter. Validation code below does the job.

 

    def updateParameters(self):
        # Modify parameter values and properties.
        # This gets called each time a parameter is modified, before 
        # standard validation.
        if self.params[0].altered and self.params[0].value:
            source_field_list = [f.name for f in arcpy.ListFields(self.params[0].value)]
            self.params[2].filters[0].list = source_field_list
            
        if self.params[1].altered and self.params[1].value:
            target_field_list = [f.name for f in arcpy.ListFields(self.params[1].value)]
            self.params[2].filters[1].list = target_field_list
        return

[PhilLarkin1]

Thanks for posting this. ESRI should consider adding this to their help documentation. Without having preset filters created you can't set them via arcpy. 

    def initializeParameters(self):
  
        self.params[0].filters[0].list = ['test']

# error returned: AttributeError: ParameterObject: Get attribute: filters does not exist

Help doc states the following, which isn't true from arcpy. If you add a list to a ValueTable that doesn't have a filter predefined you get errors.
 
By adding values to an empty filter, you activate the filter, and the user's choices are limited by the contents of the filter. (link)