Problem getting value from arcpy script tool with validation code driven drop-down: code window popup on tool execution

Question

I am attempting to provide the user a drop down list of field values based on a predefined shapefile or table. The string value users choose then needs to be taken by the script tool for use later in the script.

I have the 'drop down' value list dynamically populated using the following validation code:

def updateParameters(self):
   self.params[2].filter.list = [str(val) for val in sorted(set(row.getValue('FC_field') for row in arcpy.SearchCursor("FC_path",None, None, 'FC_field')))]
   return

I then have the following script tool code which attempts to retrieve and store that value:

#---Import system modules.---
import arcpy

ProjectName = arcpy.GetParameterAsText(0)           
ProjectBoundaries_FC = arcpy.GetParameterAsText(1)  
Airport = arcpy.GetParameterAsText(2)

arcpy.AddMessage("INPUT: Project Name (0): <" + ProjectName + ">.")
arcpy.AddMessage("INPUT: Project boundaries (1): <" + ProjectBoundaries_FC + ">.")
arcpy.AddMessage("INPUT: Project Airport (2): <" + Airport + ">.")

The tool Parameters are set according to the image:

When the script tool is executed the text editor window pops up (illustrated below). Once I close it the tool processing bar stops and the rest of the code which would utilize that value never runs. In other words, when I close the editor window the script tool reports processing completed without errors, but never processes the "AddMessage" code (illustrated in the following image).

I suspect this is largely due to my unfamiliarity with using validation code.

As requested, here is a screenshot of the tool window showing the tool parameter options in use.

I am using ArcGIS v10.1 for Desktop - Advanced (ArcInfo) License

I think the most interesting thing here is why the tools script pops up in the text pad editor window at all?

Answer 1

A couple of things might be happening that may slow things down, or their may be ways to speed it up. Although, validation in my experience is always slow.

For one, since you are using ArcPy 10.1, switch to the da module for your search cursor. This module tends to process data faster than the original SearchCursor (arcpy.da.SearchCursor). You will need to change your code slightly as for this.

Also, you may want to add an if statement to check that the path to your feature class has been altered if not self.params[0].altered:....It might be trying to update your list of values anytime you click the tool with your mouse. You could also add a check to see if the feature class exists (arcpy.exists()), and that the field you are searching for exists.

for the da module: http://pro.arcgis.com/en/pro-app/arcpy/data-access/searchcursor-class.htm

The arcpy.da cursors (arcpy.da.SearchCursor, arcpy.da.UpdateCursor, and arcpy.da.InsertCursor) were introduced with ArcGIS 10.1 to provide significantly faster performance over the previously existing set of cursor functions (arcpy.SearchCursor, arcpy.UpdateCursor, and arcpy.InsertCursor). The original cursors are provided only for continuing backward compatibility.

Answer 2

Ok, so the solution is quite silly in hindsight! The problem was never with validation or the script itself. Recently I've been just coding in a text pad because I've been in and out of the office. I forgot to change the file extension to .py from a .txt. The .txt was what was being referenced by the script tool.