Optional script input parameters

Question

I have created a script (see below) that works ok but only in case if all parameters are required inputs. Quite simple, Roads(line) and Trackts(polygon) feature classes , first buffer Roads and then clip to Tracts. There are more feature classes in Zion.gdb but I am just doing a test script to figure out optional input parameters.

What I need is that user should be able to select the layer they want to buffer, the layer they want to clip, the output location/name of the clip, and the buffer distance. All of it has to be optional. The problem is when I set for example Tracts and Tracts_Clip feature classes to optional in Script Parameters and do not apply them in script execution because I want only Roads buffer, the script does not work.

enter image description here enter image description here

import arcpy
from arcpy import env
 # set environment settings
 env.workspace = "C:/data/Zion.gdb"
 env.overwriteOutput = True
 # Script arguments
 Roads = arcpy.GetParameterAsText(0)
 if Roads == '#' or not Roads: 
 Roads = arcpy.GetParameterAsText(0) # provide a default value if unspecified
 Tracts = arcpy.GetParameterAsText(1)
 if Tracts == '#' or not Tracts:
 Tracts = arcpy.GetParameterAsText(1) # provide a default value if unspecified
 Tracts_Clip = arcpy.GetParameterAsText(2)
 if Tracts_Clip == '#' or not Tracts_Clip:
 Tracts_Clip = arcpy.GetParameterAsText(2) # provide a default value if unspecified
 Buffer_Distance = arcpy.GetParameterAsText(3)
 if Buffer_Distance == '#' or not Buffer_Distance:
 Buffer_Distance = arcpy.GetParameterAsText(3) # provide a default value if unspecified
 # Local variables:
 Tracts_Clip = arcpy.GetParameterAsText(2)
 Buffer_Distance = arcpy.GetParameterAsText(3)
 Roads_Buffer = "Roads_Buffer"
 # Process: Buffer
 arcpy.Buffer_analysis(Roads, Roads_Buffer, Buffer_Distance,"FULL", "ROUND", "ALL", "", "")
 # Process: Clip (1)
 arcpy.Clip_analysis(Tracts, Roads_Buffer, Tracts_Clip, "")

• Adam: you can est your defaults in the parameter tab of the tool properties, rather than needing to do it in the script.

Answer 1

You can build a simple logic testing whether user has provided any value for each of parameters:

import arcpy
Roads = arcpy.GetParameterAsText(0)
Tracts = arcpy.GetParameterAsText(1)
roads_def = 'path to feature class'
tracts_def = 'path to feature class'
if Roads:
 arcpy.AddMessage(Roads)
else:
 arcpy.AddMessage('No parameter1 value; using {}'.format(roads_def))
 Roads = roads_def
if Tracts:
 arcpy.AddMessage(Tracts)
else:
 arcpy.AddMessage('No parameter2 value; using {}'.format(tracts_def))
 Tracts = tracts_def

Alternatively, you could use

• ToolValidator class to update parameters values after user has provided a value for one or more other parameters;
• Use default value associated with each of the parameters that user will see when starting the tool.