Returning value from ArcGIS Pro custom tool (.py)

Question

How do we return a value from a custom .py tool, so that when I run the tool in another script, it will return a value (such as a number, string, or tuple)?

Notice in the execute class function, I attempt to return a tuple of values (trying both arcpy.SetParameter and return). However, when I run the tool in a separate script, the return value is None.

I use the following code to import the toolbox and run the code:

arcpy.ImportToolbox(pyt_path, "myToolbox")
result = arcpy.myToolbox.HelloWorld()

Below is an example .py script for the tool above

import arcpy
class HelloWorld(object):
 def __init__(self):
 """Define the tool (tool name is the name of the class)."""
 self.label = "Hello World"
 self.description = ""
 self.canRunInBackground = False
 def getParameterInfo(self):
 
 """Define parameter definitions"""
 param1 = arcpy.Parameter(
 displayName="output",
 name="outparam",
 datatype="GPString",
 parameterType="Derived",
 direction="Output")
 return [param1]
 def isLicensed(self):
 """Set whether 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."""
 return
 def updateMessages(self, parameters):
 """Modify the messages created by internal validation for each tool
 parameter. This method is called after internal validation."""
 return
 def execute(self, parameters, messages):
 """The source code of the tool.""" 
 arcpy.AddMessage("Hello World!")
 arcpy.SetParameter(0, "Hello world")
 return "Hello world"
 def postExecute(self, parameters):
 """This method takes place after outputs are processed and
 added to the display."""
 return

Below is my .pyt file

from HelloWorld import HelloWorld
class Toolbox(object):
 def __init__(self):
 """Define the toolbox (the name of the toolbox is the name of the .pyt file)."""
 self.label = 'Test TBX'
 self.alias = 'TestTBX'
 # List of Tool classes associated with this toolbox
 self.tools = [HelloWorld]

---

Here is a regular arcpy example using their Spatial Analyst toolbox. I would like to get a return value as well with my custom tool.

# Import system modules
import arcpy
from arcpy import env
from arcpy.sa import Basin
# Set environment settings
env.workspace = "C:/Path/To/Data"
# Set local variables
inFlowDirectionRaster = "flowdir"
# Execute FlowDirection
outBasin = Basin(inFlowDirectionRaster)

• Hornbydd: Read the help file on SetParameter()
• Clouseau: I tried that option and I could not get it to work. I will edit my code to add that example.
• Hornbydd: Now I see your example code, I repeat read the help file, you are making up syntax that does not exist. Look at the sample code on the help page.
• Clouseau: I forgot to include the update to the getParameterInfo function. Other than that, I am unsure of how to move forward.
• user2856: I'm not seeing anywhere in your examples where you run the HelloWorld tool?

Answer 1

Your code worked fine for me returning the text Hello world. My script was:

arcpy.ImportToolbox(r"C:\Temp\ORN\t2.pyt","TestTBX" )
res = arcpy.TestTBX.HelloWorld()
print(res.getOutput(0))

The only things I did was to ensure the HelloWorld.py file was in the same folder as the PYT file and removed the text after the return statement in the execute function; you do not need that as you are passing out the text through the SetParameter(), which you are now correctly defining.