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.

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, "")

you can est your defaults in the parameter tab of the tool properties, rather than needing to do it in the script. — Adam
– Adam, Commented Mar 13, 2017 at 22:53

Alex Tereshenkov · Accepted Answer · 2017-03-26 18:23:39Z

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.

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